From FreeCAD Documentation
- Select any combination of two elements: vertices, edges, faces
- There are several ways to invoke the command:
- Press the Measure Linear button.
- Select the Measure → Measure Linear option from the menu.
- Alternatively the command can be launched without prior selection. A selection dialog then opens in the Task panel. A Control widget also provides buttons to reset the selection, toggle the measurement display in the 3D view, and clear all measurements.
- Measurements are automatically discarded when closing the document.