Unlike QGIS, the QField measure tool does not allow the choice of ellipsoidal or cartesian distances. Apparently, it calculates ellipsoidal distances. For projects that are based on a cartesian grid (e.g. UTM), this can be a source of error or confusion, or at least cause the user to have to do extra calculations involving a scale factor.

There should be a setting to choose whether ellipsoidal or cartesian calculations are performed.

Along with affecting the calculation of distances, the setting should also affect the calculations of the measure tool's other results as well (azimuth, perimeter, and area).