# Using M value to calculate duration seems to cause some issues **URL:** \ **Category:** Advanced Use & Customization\ **Created:** [5 March 2026 16:30 UTC](https://community.qfield.org/t/using-m-value-to-calculate-duration-seems-to-cause-some-issues/1513 "2026-03-05T16:30:13Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Jeroen-GroeneBij](https://dub1.discourse-cdn.com/flex018/user_avatar/community.qfield.org/jeroen-groenebij/32/905_2.png) [@Jeroen-GroeneBij](https://community.qfield.org/u/Jeroen-GroeneBij)\ **Post date:** [5 March 2026 16:30 UTC](https://community.qfield.org/t/using-m-value-to-calculate-duration-seems-to-cause-some-issues/1513/1 "2026-03-05T16:30:13Z")
Hi, I have no idea if this turns out to be a bug or something else. I am trying to get a duration for tracked routes using the following: I have a geopackage with a Linestring layer and I have Include M values ticked when creating the layer. In this layer the line objects from Tracking are stored. One of the fields (integer type) is called duration. I would like to populate this field with the duration of the track, so I use the expression ```auto m(end_point(@geometry)) ``` This will return the m value of the last vertex and with the default QField tracking setting for m values (elapsed time), this gives me the duration. Now, when I use this expression in the Attributes Form as Default value (with or without checking the Apply default on update box), QField is having problems with the internal positioning in such a way that it thinks my position is at random times suddenly more than 50 meters away and jumping back. When I remove the default setting in the Attributes form, QField seems to be okay. I notice no weird behaviour. M values are being stored, so I can add duration afterwards in QGIS. Could it be that the expression using end\_point(@geometry) has an issue with tracking where end\_point might no be clear all the time? This is on a google pixel 8 phone and QField 4.0.5