adding more nodes

docs/nodes/Multiple Profiles.md

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+# Multiple Profiles
+
+Extract and compare line profiles from two fields along a chosen row or column. Supports overlay, mean, and difference modes. Equivalent to Gwyddion's multiprofile.c module.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field_a | DATA_FIELD | Yes | First input field |
+| field_b | DATA_FIELD | Yes | Second input field |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| profile | LINE_DATA | Resulting line profile |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| row | INT | -1 | Row (horizontal) or column (vertical) index to extract; -1 uses the centre row/column (-1–10000) |
+| direction | dropdown | horizontal | Profile direction: horizontal (extract a row) or vertical (extract a column) |
+| mode | dropdown | overlay | Combination mode: overlay (field_a profile only), mean (average of both), or difference (field_a minus field_b) |
+
+## Notes
+
+- When the two fields have different sizes, profiles are truncated to the shorter length so they can be compared element-wise.
+- The x-axis of the output profile uses physical spacing (dx for horizontal, dy for vertical) from field_a.
+- The output y-unit inherits field_a's z-unit.
+- Difference mode is useful for visualising drift, processing artefacts, or changes between sequential scans.