diff --git a/backend/nodes/arc_revolve.py b/backend/nodes/arc_revolve.py
new file mode 100644
index 0000000..d7edb99
--- /dev/null
+++ b/backend/nodes/arc_revolve.py
@@ -0,0 +1,88 @@
+"""Arc Revolve — subtract a cylindrical arc background."""
+
+from __future__ import annotations
+
+import numpy as np
+
+from backend.node_registry import register_node
+from backend.data_types import DataField
+
+
+def _arc_kernel(radius: int) -> np.ndarray:
+    """Build a 1D arc kernel: z = 1 - sqrt(1 - (i/radius)^2)."""
+    half = min(radius, 4096)
+    i = np.arange(-half, half + 1, dtype=np.float64)
+    t = np.clip((i / radius) ** 2, 0.0, 1.0)
+    return 1.0 - np.sqrt(1.0 - t)
+
+
+def _arc_revolve_1d(data: np.ndarray, radius: int) -> np.ndarray:
+    """Compute arc-revolve background for each row independently."""
+    yres, xres = data.shape
+    kernel = _arc_kernel(radius)
+    half = len(kernel) // 2
+    bg = np.empty_like(data)
+
+    for row in range(yres):
+        line = data[row].copy()
+        # Suppress deep outliers before fitting
+        window = min(half, xres // 2)
+        if window > 0:
+            from scipy.ndimage import uniform_filter1d
+            local_mean = uniform_filter1d(line, size=2 * window + 1, mode='nearest')
+            local_sq = uniform_filter1d(line ** 2, size=2 * window + 1, mode='nearest')
+            local_rms = np.sqrt(np.maximum(local_sq - local_mean ** 2, 0.0))
+            threshold = local_mean - 2.5 * np.maximum(local_rms, 1e-30)
+            line = np.maximum(line, threshold)
+
+        # For each pixel, find the lowest position the arc can sit
+        padded = np.pad(line, half, mode='edge')
+        row_bg = np.full(xres, np.inf)
+        for k in range(len(kernel)):
+            shifted = padded[k:k + xres] - kernel[k]
+            row_bg = np.minimum(row_bg, shifted)
+        bg[row] = row_bg
+
+    return bg
+
+
+@register_node(display_name="Arc Revolve")
+class ArcRevolve:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+                "radius": ("INT", {"default": 20, "min": 1, "max": 1000, "step": 1}),
+                "direction": (["horizontal", "vertical", "both"], {"default": "horizontal"}),
+            }
+        }
+
+    OUTPUTS = (
+        ('DATA_FIELD', 'leveled'),
+        ('DATA_FIELD', 'background'),
+    )
+    FUNCTION = "process"
+
+    DESCRIPTION = (
+        "Subtract a cylindrical arc background. A circular arc of the given "
+        "radius is rolled under each row (or column), and the envelope it "
+        "traces out is subtracted as the background."
+    )
+
+    KEYWORDS = ("arc", "revolve", "cylindrical", "background", "level")
+
+    def process(self, field: DataField, radius: int = 20,
+                direction: str = "horizontal") -> tuple:
+        data = np.asarray(field.data, dtype=np.float64)
+
+        if direction == "horizontal":
+            bg = _arc_revolve_1d(data, radius)
+        elif direction == "vertical":
+            bg = _arc_revolve_1d(data.T, radius).T
+        else:
+            bg_h = _arc_revolve_1d(data, radius)
+            bg_v = _arc_revolve_1d(data.T, radius).T
+            bg = np.minimum(bg_h, bg_v)
+
+        return (field.replace(data=data - bg), field.replace(data=bg))
diff --git a/backend/nodes/level_rotate.py b/backend/nodes/level_rotate.py
new file mode 100644
index 0000000..011396c
--- /dev/null
+++ b/backend/nodes/level_rotate.py
@@ -0,0 +1,75 @@
+"""Level Rotate — level by physically rotating the data plane."""
+
+from __future__ import annotations
+
+import numpy as np
+from scipy.ndimage import map_coordinates
+
+from backend.node_registry import register_node
+from backend.data_types import DataField
+
+
+@register_node(display_name="Level Rotate")
+class LevelRotate:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+            }
+        }
+
+    OUTPUTS = (
+        ('DATA_FIELD', 'leveled'),
+    )
+    FUNCTION = "process"
+
+    DESCRIPTION = (
+        "Level by physically rotating the data plane. Fits a best-fit plane, "
+        "converts its slopes to tilt angles, then rotates the surface by "
+        "those angles using interpolation rather than algebraic subtraction."
+    )
+
+    KEYWORDS = ("rotate", "tilt", "level", "plane")
+
+    def process(self, field: DataField) -> tuple:
+        data = np.asarray(field.data, dtype=np.float64)
+        yres, xres = data.shape
+
+        # Fit plane: z = a + bx*x + by*y (x,y in pixel coords)
+        yy, xx = np.mgrid[:yres, :xres].astype(np.float64)
+        A = np.column_stack([np.ones(yres * xres), xx.ravel(), yy.ravel()])
+        coeffs, _, _, _ = np.linalg.lstsq(A, data.ravel(), rcond=None)
+        _, bx, by = coeffs
+
+        # Convert pixel slopes to tilt angles
+        alpha_x = np.arctan(bx)
+        alpha_y = np.arctan(by)
+
+        # Build rotation: for each output pixel, find where it came from
+        cx = (xres - 1) / 2.0
+        cy = (yres - 1) / 2.0
+
+        cos_x = np.cos(alpha_x)
+        cos_y = np.cos(alpha_y)
+
+        # Source coordinates after removing tilt
+        src_x = xx.copy()
+        src_y = yy.copy()
+        src_z = data.copy()
+
+        # Rotate about x-axis (corrects y-tilt)
+        dy = yy - cy
+        src_y_rot = cy + dy * cos_y
+        src_z = src_z - dy * np.sin(alpha_y)
+
+        # Rotate about y-axis (corrects x-tilt)
+        dx = xx - cx
+        src_x_rot = cx + dx * cos_x
+        src_z = src_z - dx * np.sin(alpha_x)
+
+        # Resample with the adjusted z values
+        result = map_coordinates(src_z, [src_y_rot, src_x_rot], order=1,
+                                 mode='nearest')
+
+        return (field.replace(data=result),)
diff --git a/backend/nodes/sphere_revolve.py b/backend/nodes/sphere_revolve.py
new file mode 100644
index 0000000..7c1e39c
--- /dev/null
+++ b/backend/nodes/sphere_revolve.py
@@ -0,0 +1,74 @@
+"""Sphere Revolve — subtract a spherical cap background."""
+
+from __future__ import annotations
+
+import numpy as np
+from scipy.ndimage import uniform_filter
+
+from backend.node_registry import register_node
+from backend.data_types import DataField
+
+
+def _sphere_kernel(radius: int) -> np.ndarray:
+    """Build a 2D spherical cap kernel."""
+    half = min(radius, 512)
+    i = np.arange(-half, half + 1, dtype=np.float64)
+    ii, jj = np.meshgrid(i, i)
+    r2 = (ii ** 2 + jj ** 2) / (radius ** 2)
+    r2 = np.clip(r2, 0.0, 1.0)
+    return 1.0 - np.sqrt(1.0 - r2)
+
+
+@register_node(display_name="Sphere Revolve")
+class SphereRevolve:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+                "radius": ("INT", {"default": 20, "min": 1, "max": 500, "step": 1}),
+            }
+        }
+
+    OUTPUTS = (
+        ('DATA_FIELD', 'leveled'),
+        ('DATA_FIELD', 'background'),
+    )
+    FUNCTION = "process"
+
+    DESCRIPTION = (
+        "Subtract a spherical cap background. A sphere of the given radius "
+        "is rolled under the surface, and the envelope it traces is "
+        "subtracted as the background."
+    )
+
+    KEYWORDS = ("sphere", "revolve", "spherical", "background", "level")
+
+    def process(self, field: DataField, radius: int = 20) -> tuple:
+        data = np.asarray(field.data, dtype=np.float64)
+        yres, xres = data.shape
+
+        kernel = _sphere_kernel(radius)
+        half = kernel.shape[0] // 2
+
+        # Suppress deep outliers
+        window = max(1, half // 2)
+        local_mean = uniform_filter(data, size=2 * window + 1, mode='nearest')
+        local_sq = uniform_filter(data ** 2, size=2 * window + 1, mode='nearest')
+        local_rms = np.sqrt(np.maximum(local_sq - local_mean ** 2, 0.0))
+        threshold = local_mean - 2.5 * np.maximum(local_rms, 1e-30)
+        clipped = np.maximum(data, threshold)
+
+        padded = np.pad(clipped, half, mode='edge')
+        bg = np.full_like(data, np.inf)
+
+        ks = kernel.shape[0]
+        for di in range(ks):
+            for dj in range(ks):
+                k_val = kernel[di, dj]
+                if k_val >= 1.0:
+                    continue
+                shifted = padded[di:di + yres, dj:dj + xres] - k_val
+                bg = np.minimum(bg, shifted)
+
+        return (field.replace(data=data - bg), field.replace(data=bg))
diff --git a/backend/nodes/unrotate.py b/backend/nodes/unrotate.py
new file mode 100644
index 0000000..bb55188
--- /dev/null
+++ b/backend/nodes/unrotate.py
@@ -0,0 +1,88 @@
+"""Unrotate — auto-detect and correct in-plane scan rotation."""
+
+from __future__ import annotations
+
+import numpy as np
+from scipy.ndimage import rotate as ndimage_rotate
+
+from backend.node_registry import register_node
+from backend.data_types import DataField
+
+
+def _slope_angle_histogram(data: np.ndarray, n_bins: int = 3600) -> np.ndarray:
+    """Compute histogram of local slope angles over [0, 2*pi)."""
+    dy = np.diff(data, axis=0)[:, :-1]
+    dx = np.diff(data, axis=1)[:-1, :]
+    angles = np.arctan2(dy, dx) % (2 * np.pi)
+    hist, _ = np.histogram(angles.ravel(), bins=n_bins, range=(0, 2 * np.pi))
+    return hist.astype(np.float64)
+
+
+def _find_dominant_angle(hist: np.ndarray, symmetry: int) -> float:
+    """Find the rotation correction angle for a given symmetry order.
+
+    Folds the histogram into one symmetry sector, finds the peak, and
+    returns the offset to the nearest axis.
+    """
+    n_bins = len(hist)
+    sector = n_bins // symmetry
+    folded = np.zeros(sector, dtype=np.float64)
+    for k in range(symmetry):
+        start = k * sector
+        end = start + sector
+        if end <= n_bins:
+            folded += hist[start:end]
+
+    peak_bin = int(np.argmax(folded))
+    bin_angle = (2 * np.pi / symmetry) / sector
+
+    # The angle of the peak
+    peak_angle = peak_bin * bin_angle
+
+    # The nearest axis is at multiples of pi/symmetry
+    axis_spacing = np.pi / symmetry
+    nearest_axis = round(peak_angle / axis_spacing) * axis_spacing
+    correction = nearest_axis - peak_angle
+
+    return float(correction)
+
+
+@register_node(display_name="Unrotate")
+class Unrotate:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+                "symmetry": (["2-fold", "3-fold", "4-fold", "6-fold"], {"default": "4-fold"}),
+            }
+        }
+
+    OUTPUTS = (
+        ('DATA_FIELD', 'leveled'),
+    )
+    FUNCTION = "process"
+
+    DESCRIPTION = (
+        "Auto-detect and correct in-plane scan rotation. Computes a slope "
+        "angle histogram, finds the dominant feature direction for the given "
+        "symmetry, and rotates the image to align features with the axes."
+    )
+
+    KEYWORDS = ("rotation", "alignment", "angle", "symmetry", "crystal")
+
+    def process(self, field: DataField, symmetry: str = "4-fold") -> tuple:
+        data = np.asarray(field.data, dtype=np.float64)
+
+        sym_order = int(symmetry[0])
+        hist = _slope_angle_histogram(data)
+        angle_rad = _find_dominant_angle(hist, sym_order)
+        angle_deg = float(np.degrees(angle_rad))
+
+        if abs(angle_deg) < 0.01:
+            return (field,)
+
+        rotated = ndimage_rotate(data, angle_deg, reshape=False, order=1,
+                                 mode='nearest')
+
+        return (field.replace(data=rotated),)
diff --git a/backend/nodes/zero_value.py b/backend/nodes/zero_value.py
new file mode 100644
index 0000000..a2de5f3
--- /dev/null
+++ b/backend/nodes/zero_value.py
@@ -0,0 +1,56 @@
+"""Zero Value — shift data so the mean or maximum equals zero."""
+
+from __future__ import annotations
+
+import numpy as np
+
+from backend.node_registry import register_node
+from backend.data_types import DataField
+
+
+@register_node(display_name="Zero Mean")
+class ZeroMean:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+            }
+        }
+
+    OUTPUTS = (
+        ('DATA_FIELD', 'leveled'),
+    )
+    FUNCTION = "process"
+
+    DESCRIPTION = "Shift all values so the mean is exactly zero."
+
+    KEYWORDS = ("offset", "center", "level", "mean")
+
+    def process(self, field: DataField) -> tuple:
+        data = np.asarray(field.data, dtype=np.float64)
+        return (field.replace(data=data - data.mean()),)
+
+
+@register_node(display_name="Zero Maximum")
+class ZeroMaximum:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "field": ("DATA_FIELD",),
+            }
+        }
+
+    OUTPUTS = (
+        ('DATA_FIELD', 'leveled'),
+    )
+    FUNCTION = "process"
+
+    DESCRIPTION = "Shift all values so the maximum is exactly zero."
+
+    KEYWORDS = ("offset", "level", "maximum")
+
+    def process(self, field: DataField) -> tuple:
+        data = np.asarray(field.data, dtype=np.float64)
+        return (field.replace(data=data - data.max()),)
diff --git a/docs/missing_gwyddion_features.md b/docs/missing_gwyddion_features.md
new file mode 100644
index 0000000..e5fc1b7
--- /dev/null
+++ b/docs/missing_gwyddion_features.md
@@ -0,0 +1,98 @@
+# Missing Gwyddion Features
+
+Gwyddion 2D image/surface processing features not yet implemented in tono. Excludes force curves, force volume, spectroscopy, volume data, XYZ data, graph operations, and file I/O.
+
+## Leveling / Background Removal
+
+- [x] **Arc Revolve** — Subtract cylindrical arc background fitted by revolving an arc under the data
+- [x] **Sphere Revolve** — Subtract spherical cap background
+- [x] **Unrotate** — Auto-detect and correct in-plane scan rotation by finding dominant feature directions
+- [x] **Level Rotate** — Level by physically rotating the data plane rather than subtracting a polynomial
+- [x] **Zero Mean Value** — Shift all values so the mean is exactly zero (pure offset, no plane fit)
+- [x] **Zero Maximum Value** — Shift all values so the maximum is exactly zero
+
+## Filtering / Signal Processing
+
+- [ ] **2D CWT** — Continuous Wavelet Transform for scale-space analysis
+- [ ] **XY Denoise** — Denoise by combining two orthogonal scans (forward/backward or horizontal/vertical)
+- [ ] **Rank Presentation** — Rank transform image for local contrast enhancement
+- [ ] **Radial Smoothing** — Smooth data in polar coordinates, averaging along radial or angular direction
+- [ ] **Convolve Two Images** — Convolve two separate data channels together
+
+## Line Correction / Scan Artifacts
+
+- [ ] **Step Block Correction** — Correct vertical step offsets between scan lines by block-matching
+- [ ] **Good Mean Profile** — Compute a high-quality average scan line from repeated scans
+- [ ] **Align Rows (extended methods)** — Modus and Gaussian-weighted row alignment beyond tono's current set
+
+## Correction / Restoration
+
+- [ ] **Fractal Correction** — Fill masked/bad pixels using fractal interpolation (alternative to Laplace)
+- [ ] **Correlation Averaging** — Average repeated similar structures using autocorrelation alignment
+- [ ] **Coerce** — Force data to match the histogram distribution of another dataset
+- [ ] **Periodic Translate** — Translate image data treating the field as periodic (wrap-around shift)
+- [ ] **Reorder** — Reorder pixel rows/columns (interleaved to sequential, reverse scan, etc.)
+
+## Statistical Analysis
+
+- [ ] **Transfer Function Fit** — Fit PSF from a known reference image and a measured blurred image
+- [ ] **Transfer Function Guess** — Estimate PSF from a single image without a reference
+- [ ] **Angle Distribution** — Distribution of surface normal angles (distinct from slope distribution)
+
+## Grain Operations
+
+- [ ] **Otsu Threshold** — Automated grain/mask threshold using Otsu's method
+- [ ] **Remove Edge-Touching Grains** — Remove all grains touching the image border from a mask
+- [ ] **Grain Selection Shapes** — Create geometric selections (bounding boxes, inscribed discs, etc.) from grain masks
+
+## Mask Operations
+
+- [ ] **Mask Thin** — Morphological thinning to single-pixel-wide skeletons
+- [ ] **Mask Distribute** — Copy/distribute a mask to multiple channels simultaneously
+- [ ] **Mark With** — Create or modify a mask using arithmetic conditions on other channels
+
+## Basic Operations
+
+- [ ] **Invert Value** — Flip heights (z to -z)
+- [ ] **Log Scale Presentation** — Log-scaled presentation layer without modifying source data
+- [ ] **Limit Range** — Clamp data values to a specified min/max range
+- [ ] **Square Samples** — Resample so pixels are physically square (equal x/y size)
+- [ ] **Null Offsets** — Zero out the lateral (XY) origin offsets
+
+## SPM-Specific Modes
+
+- [ ] **MFM Field Simulation** — Simulate magnetic stray field above perpendicular media
+- [ ] **MFM Parallel Media** — Simulate MFM signal for in-plane magnetic media
+- [ ] **MFM Lift Shift** — Simulate MFM signal change when lift height changes
+- [ ] **MFM Lift Estimate** — Estimate lift height difference from data blur
+- [ ] **MFM Force Gradient** — Convert MFM raw data to force gradient units
+- [ ] **SMM Apply Calibration** — Apply Scanning Microwave Microscopy calibration coefficients
+
+## Synthetic Surface Generators
+
+Tono has one generic Synthetic Surface node. Gwyddion has ~20+ specialized generators:
+
+- [ ] **Fractional Brownian Motion** — fBm rough surfaces with controlled Hurst exponent
+- [ ] **Spectral Synthesis** — PSD-specified random rough surfaces
+- [ ] **Lattice** — Crystalline lattice surface with defects
+- [ ] **Objects** — Randomly placed 3D objects (spheres, pyramids, etc.)
+- [ ] **Patterns** — Geometric patterns (staircase, gratings, etc.)
+- [ ] **Waves** — Sinusoidal/wave patterns
+- [ ] **Noise** — Uncorrelated random noise with configurable distribution
+- [ ] **Line Noise** — Synthetic scan-line noise/steps/scars for testing
+- [ ] **Fibres** — Random fibre network surfaces
+- [ ] **Domain Walls** — Phase-separated domain structures
+- [ ] **Columnar Growth** — Columnar thin-film growth simulation
+- [ ] **Ball Deposition** — Random ballistic deposition growth
+- [ ] **Particle Deposition** — Dynamical particle deposition model
+- [ ] **Rod Deposition** — Rod-like particle deposition
+- [ ] **Diffusion** — Diffusion-limited aggregation surfaces
+- [ ] **Discs** — Random overlapping disc surfaces
+- [ ] **CPDE / Turing** — Reaction-diffusion / Turing pattern surfaces
+- [ ] **Sand Dunes** — Aeolian sand transport simulation
+- [ ] **Annealing Lattice Gas** — Annealed lattice-gas model textures
+- [ ] **Phase Separation** — Spinodal decomposition textures
+- [ ] **Pileup** — Piled-up ellipsoids or bars
+- [ ] **Plateaus** — Stacked random plateau/terrace structures
+- [ ] **Film Residue** — Residue left after simulated film removal
+- [ ] **Wetting Front** — Propagating wetting front simulation
diff --git a/docs/nodes/Arc Revolve.md b/docs/nodes/Arc Revolve.md
new file mode 100644
index 0000000..1c7c83d
--- /dev/null
+++ b/docs/nodes/Arc Revolve.md	
@@ -0,0 +1,29 @@
+# Arc Revolve
+
+Subtract a cylindrical arc background. A circular arc of the given radius is rolled under each row (or column), and the envelope it traces is subtracted as the background.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| leveled | DATA_FIELD | Field with arc background subtracted |
+| background | DATA_FIELD | The estimated arc background |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| radius | INT | 20 | Arc radius in pixels (1–1000) |
+| direction | dropdown | horizontal | Direction to apply the arc: horizontal, vertical, or both |
+
+## Notes
+
+- Larger radii produce smoother backgrounds that follow gentle curvature. Smaller radii track finer features.
+- The "both" direction takes the minimum of horizontal and vertical backgrounds.
+- Deep outliers are suppressed before fitting so that scratches or pits do not pull the arc down.
diff --git a/docs/nodes/Level Rotate.md b/docs/nodes/Level Rotate.md
new file mode 100644
index 0000000..ec749c5
--- /dev/null
+++ b/docs/nodes/Level Rotate.md	
@@ -0,0 +1,21 @@
+# Level Rotate
+
+Level by physically rotating the data plane. Fits a best-fit plane, converts its slopes to tilt angles, then rotates the surface by those angles using interpolation rather than algebraic subtraction.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field to level |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| leveled | DATA_FIELD | Field with tilt removed by rotation |
+
+## Notes
+
+- Unlike Plane Level (which subtracts a fitted plane), this node rotates the 3D surface to make it horizontal. The distinction matters for steep tilts where subtraction introduces distortion.
+- Uses bilinear interpolation to resample rotated z-values.
+- Edges are handled with nearest-neighbor extension.
diff --git a/docs/nodes/Sphere Revolve.md b/docs/nodes/Sphere Revolve.md
new file mode 100644
index 0000000..156095a
--- /dev/null
+++ b/docs/nodes/Sphere Revolve.md	
@@ -0,0 +1,28 @@
+# Sphere Revolve
+
+Subtract a spherical cap background. A sphere of the given radius is rolled under the surface, and the envelope it traces is subtracted as the background.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| leveled | DATA_FIELD | Field with spherical background subtracted |
+| background | DATA_FIELD | The estimated spherical background |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| radius | INT | 20 | Sphere radius in pixels (1–500) |
+
+## Notes
+
+- Works like Arc Revolve but in two dimensions — suitable for bowl-shaped or dome-shaped backgrounds.
+- Larger radii produce smoother backgrounds. Very small radii will track individual features.
+- Deep outliers are suppressed before fitting.
diff --git a/docs/nodes/Unrotate.md b/docs/nodes/Unrotate.md
new file mode 100644
index 0000000..12f3997
--- /dev/null
+++ b/docs/nodes/Unrotate.md
@@ -0,0 +1,28 @@
+# Unrotate
+
+Auto-detect and correct in-plane scan rotation. Computes a slope angle histogram, finds the dominant feature direction for the given symmetry, and rotates the image to align features with the axes.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field to correct |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| leveled | DATA_FIELD | Field with rotation corrected |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| symmetry | dropdown | 4-fold | Expected symmetry of the surface features: 2-fold, 3-fold, 4-fold, or 6-fold |
+
+## Notes
+
+- Best suited for crystalline or patterned surfaces where features have a clear preferred direction.
+- 4-fold symmetry is the most common choice for cubic crystal surfaces and rectangular gratings.
+- If the detected rotation is less than 0.01°, the data is returned unchanged.
+- Uses bilinear interpolation; edges are handled with nearest-neighbor extension.
diff --git a/docs/nodes/Zero Maximum.md b/docs/nodes/Zero Maximum.md
new file mode 100644
index 0000000..b8c0d99
--- /dev/null
+++ b/docs/nodes/Zero Maximum.md	
@@ -0,0 +1,20 @@
+# Zero Maximum
+
+Shift all values so the maximum is exactly zero. All resulting values will be zero or negative.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field to level |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| leveled | DATA_FIELD | Field with maximum subtracted |
+
+## Notes
+
+- Equivalent to subtracting the global maximum from every pixel.
+- Useful when the highest point should represent the zero reference.
diff --git a/docs/nodes/Zero Mean.md b/docs/nodes/Zero Mean.md
new file mode 100644
index 0000000..b8d0f1f
--- /dev/null
+++ b/docs/nodes/Zero Mean.md	
@@ -0,0 +1,20 @@
+# Zero Mean
+
+Shift all values so the mean is exactly zero. A pure offset subtraction — no plane fit or polynomial involved.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field to level |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| leveled | DATA_FIELD | Field with mean subtracted |
+
+## Notes
+
+- Equivalent to subtracting a constant (the mean) from every pixel.
+- Does not change relative height differences — only shifts the overall offset.
diff --git a/tests/node_tests/arc_revolve.py b/tests/node_tests/arc_revolve.py
new file mode 100644
index 0000000..2c3fe11
--- /dev/null
+++ b/tests/node_tests/arc_revolve.py
@@ -0,0 +1,55 @@
+import numpy as np
+from tests.node_tests._shared import make_field
+
+
+def test_arc_revolve_horizontal():
+    from backend.nodes.arc_revolve import ArcRevolve
+
+    node = ArcRevolve()
+    rng = np.random.default_rng(42)
+    x = np.linspace(0, 1, 64)
+    bow = 10.0 * x ** 2
+    data = bow[None, :] + rng.standard_normal((64, 64)) * 0.01
+    field = make_field(data=data)
+
+    leveled, bg = node.process(field, radius=40, direction="horizontal")
+    assert leveled.data.shape == field.data.shape
+    assert bg.data.shape == field.data.shape
+    assert np.allclose(leveled.data + bg.data, data)
+
+
+def test_arc_revolve_vertical():
+    from backend.nodes.arc_revolve import ArcRevolve
+
+    node = ArcRevolve()
+    y = np.linspace(0, 1, 64)
+    data = (5.0 * y ** 2)[:, None] * np.ones((1, 64))
+    field = make_field(data=data)
+
+    leveled, bg = node.process(field, radius=40, direction="vertical")
+    assert np.allclose(leveled.data + bg.data, data)
+
+
+def test_arc_revolve_both():
+    from backend.nodes.arc_revolve import ArcRevolve
+
+    node = ArcRevolve()
+    y, x = np.mgrid[:32, :32] / 32.0
+    data = 5.0 * x ** 2 + 3.0 * y ** 2
+    field = make_field(data=data)
+
+    leveled, bg = node.process(field, radius=30, direction="both")
+    assert leveled.data.shape == data.shape
+    assert bg.data.shape == data.shape
+
+
+def test_arc_revolve_flat_passthrough():
+    from backend.nodes.arc_revolve import ArcRevolve
+
+    node = ArcRevolve()
+    data = np.ones((32, 32)) * 5.0
+    field = make_field(data=data)
+
+    leveled, bg = node.process(field, radius=20, direction="horizontal")
+    assert leveled.data.std() < 1e-10
+    assert np.allclose(leveled.data + bg.data, data)
diff --git a/tests/node_tests/level_rotate.py b/tests/node_tests/level_rotate.py
new file mode 100644
index 0000000..650cc6f
--- /dev/null
+++ b/tests/node_tests/level_rotate.py
@@ -0,0 +1,37 @@
+import numpy as np
+from tests.node_tests._shared import make_field
+
+
+def test_level_rotate_removes_tilt():
+    from backend.nodes.level_rotate import LevelRotate
+
+    node = LevelRotate()
+    y, x = np.mgrid[:64, :64].astype(np.float64)
+    data = 2.0 * x + 3.0 * y
+    field = make_field(data=data)
+
+    (result,) = node.process(field)
+    assert result.data.shape == data.shape
+    assert result.data.std() < data.std() * 0.25
+
+
+def test_level_rotate_preserves_shape():
+    from backend.nodes.level_rotate import LevelRotate
+
+    node = LevelRotate()
+    data = np.random.default_rng(42).standard_normal((48, 48))
+    field = make_field(data=data)
+
+    (result,) = node.process(field)
+    assert result.data.shape == (48, 48)
+
+
+def test_level_rotate_flat_noop():
+    from backend.nodes.level_rotate import LevelRotate
+
+    node = LevelRotate()
+    data = np.ones((32, 32)) * 7.0
+    field = make_field(data=data)
+
+    (result,) = node.process(field)
+    assert np.allclose(result.data, 7.0, atol=1e-6)
diff --git a/tests/node_tests/sphere_revolve.py b/tests/node_tests/sphere_revolve.py
new file mode 100644
index 0000000..e554ef8
--- /dev/null
+++ b/tests/node_tests/sphere_revolve.py
@@ -0,0 +1,41 @@
+import numpy as np
+from tests.node_tests._shared import make_field
+
+
+def test_sphere_revolve_basic():
+    from backend.nodes.sphere_revolve import SphereRevolve
+
+    node = SphereRevolve()
+    y, x = np.mgrid[:64, :64] / 64.0
+    data = 10.0 * (x ** 2 + y ** 2)
+    field = make_field(data=data)
+
+    leveled, bg = node.process(field, radius=30)
+    assert leveled.data.shape == data.shape
+    assert bg.data.shape == data.shape
+    assert np.allclose(leveled.data + bg.data, data)
+
+
+def test_sphere_revolve_flat():
+    from backend.nodes.sphere_revolve import SphereRevolve
+
+    node = SphereRevolve()
+    data = np.ones((32, 32)) * 3.0
+    field = make_field(data=data)
+
+    leveled, bg = node.process(field, radius=20)
+    assert leveled.data.std() < 1e-10
+    assert np.allclose(leveled.data + bg.data, data)
+
+
+def test_sphere_revolve_outputs_two_fields():
+    from backend.nodes.sphere_revolve import SphereRevolve
+
+    node = SphereRevolve()
+    data = np.random.default_rng(7).standard_normal((32, 32))
+    field = make_field(data=data)
+
+    result = node.process(field, radius=15)
+    assert len(result) == 2
+    leveled, bg = result
+    assert np.allclose(leveled.data + bg.data, data)
diff --git a/tests/node_tests/unrotate.py b/tests/node_tests/unrotate.py
new file mode 100644
index 0000000..cfbfb8c
--- /dev/null
+++ b/tests/node_tests/unrotate.py
@@ -0,0 +1,50 @@
+import numpy as np
+from tests.node_tests._shared import make_field
+
+
+def test_unrotate_preserves_shape():
+    from backend.nodes.unrotate import Unrotate
+
+    node = Unrotate()
+    data = np.random.default_rng(42).standard_normal((64, 64))
+    field = make_field(data=data)
+
+    (result,) = node.process(field, symmetry="4-fold")
+    assert result.data.shape == (64, 64)
+
+
+def test_unrotate_small_angle():
+    from backend.nodes.unrotate import Unrotate, _slope_angle_histogram, _find_dominant_angle
+
+    y, x = np.mgrid[:128, :128].astype(np.float64)
+    angle_deg = 3.0
+    angle_rad = np.radians(angle_deg)
+    data = np.sin(2 * np.pi * (x * np.cos(angle_rad) + y * np.sin(angle_rad)) / 20.0)
+
+    hist = _slope_angle_histogram(data)
+    correction = _find_dominant_angle(hist, 4)
+    assert abs(np.degrees(correction)) < 10.0
+
+
+def test_unrotate_no_rotation_passthrough():
+    from backend.nodes.unrotate import Unrotate
+
+    node = Unrotate()
+    y, x = np.mgrid[:64, :64].astype(np.float64)
+    data = np.sin(2 * np.pi * x / 16.0)
+    field = make_field(data=data)
+
+    (result,) = node.process(field, symmetry="4-fold")
+    assert np.allclose(result.data, data, atol=0.1)
+
+
+def test_unrotate_symmetry_options():
+    from backend.nodes.unrotate import Unrotate
+
+    node = Unrotate()
+    data = np.random.default_rng(99).standard_normal((64, 64))
+    field = make_field(data=data)
+
+    for sym in ["2-fold", "3-fold", "4-fold", "6-fold"]:
+        (result,) = node.process(field, symmetry=sym)
+        assert result.data.shape == (64, 64)
diff --git a/tests/node_tests/zero_value.py b/tests/node_tests/zero_value.py
new file mode 100644
index 0000000..89874a5
--- /dev/null
+++ b/tests/node_tests/zero_value.py
@@ -0,0 +1,46 @@
+import numpy as np
+from tests.node_tests._shared import make_field
+
+
+def test_zero_mean():
+    from backend.nodes.zero_value import ZeroMean
+
+    node = ZeroMean()
+    data = np.random.default_rng(42).standard_normal((64, 64)) + 100.0
+    field = make_field(data=data)
+    (result,) = node.process(field)
+    assert result.data.shape == field.data.shape
+    assert abs(result.data.mean()) < 1e-10
+
+
+def test_zero_mean_preserves_variation():
+    from backend.nodes.zero_value import ZeroMean
+
+    node = ZeroMean()
+    data = np.random.default_rng(7).standard_normal((32, 32)) + 50.0
+    field = make_field(data=data)
+    (result,) = node.process(field)
+    assert np.allclose(result.data - result.data.mean(), data - data.mean())
+
+
+def test_zero_maximum():
+    from backend.nodes.zero_value import ZeroMaximum
+
+    node = ZeroMaximum()
+    data = np.random.default_rng(42).standard_normal((64, 64)) + 100.0
+    field = make_field(data=data)
+    (result,) = node.process(field)
+    assert result.data.shape == field.data.shape
+    assert abs(result.data.max()) < 1e-10
+    assert result.data.min() < 0
+
+
+def test_zero_maximum_preserves_differences():
+    from backend.nodes.zero_value import ZeroMaximum
+
+    node = ZeroMaximum()
+    data = np.array([[1.0, 3.0], [2.0, 5.0]])
+    field = make_field(data=data)
+    (result,) = node.process(field)
+    expected = data - 5.0
+    assert np.allclose(result.data, expected)