We are encountering issues when calibrating a PDF document using Autodesk.Measure. When we calibrate with snapping enabled at both ends, the calibration factor is approximately 72 times smaller than when we calibrate without snapping at both ends.

and it seems to be a bug when you make a calibration using snapping and not snapping. You can easily reproduce this bug. For convenience, I used this project on GitHub: Offline PDF Markup.

Step 1: Make a calibration using snapping (I use meters because I don't understand the imperial system