After the mouse button is released, the default behavior is for the measure to remain on the screen indefinitely, even when the Dynamic Measure tool is deselected. Measures are undoable, and are saved with the document. To cancel a measure in progress, press the Esc
key while moving the cursor. To constrain a measure to horizontal and vertical directions (as well as 45° increments), hold down Shift
when measuring. To snap while constraining or to constrain a measure to the general constrain angle, turn on Smart Guides.
By default, Dynamic Measure snaps the cursor to paths and guides, anchor points, and handles and draws a ring around the cursor to indicate this. When Smart Guides are enabled, Dynamic Measure will also snap to path intersections and centers, page edges, etc. A small triangle on the snapping ring(s) indicates path direction. Selected paths take precedence over unselected path when both are within snapping range.
In addition to straight-line distance, Dynamic Measure can measure the distance between two places on a path by enabling the “Distance Along Path” setting. For open paths, this measurement value is indicated by the heading ”DP:”. In the case of a closed path, there are two ways we can go “along” the path to get from the first location to the second, so the values are abbreviated as “DWP” (Distance With Path, i.e., in the direction of the path) and “DAP” (Distance Against Path, i.e. against the direction of the path):
Dynamic Measure Distance along a path