Del Sol Plan Scaler

Use calibration if the PDF is a scanned/rasterized print — click two points on any labeled dimension and enter its real length.

Desktop: left-click places points, right-click drag pans, scroll wheel zooms.
iPad / touch: tap places a point, one-finger drag pans, two-finger pinch zooms.
Click an endpoint of a finished line to resume it — new points extend that same line.
Click a middle point to snap a new line onto it exactly.
New line finishes the current run and starts a fresh one.
Undo removes the last point placed, or the last finished measurement.