When switching on auto calibration (“home” + “+”) then it shows some areas in white or red, apparently asking the user to press those. Once done so, the sensitivity of these areas is completely inconsistent. Best way to get it calibrated again seems to be to unplug and re-plug the power adapter, then the fully automatic calibration does it’s thing and it’s all good again.
Might be that just pressing on the white/red areas isn’t what is meant to be done? In that case the process could benefit from a more in depth description in the manual.