[bpye]

Yeah I think this is most likely. Then when you change the serial you're using the calibration data for the wrong screen, but most of the time you're lucky and the two screens behave close enough that an average user doesn't notice.

[can16358p]

Probably for touch the effects are negligible as the accuracy needed for touch is much more coarse compared to accuracy needed for Apple Pencil drawing. So if calibration is perfecting things at Apple Pencil-level accuracy, it should already be below the threshold of touch-based highest acceptable margin of error anyway.

[raphman]

Touch and pen would generally require completely different calibrations because touch is detected by the capacitive touch screen whereas the pen position is tracked inductively.

However, I wonder why the pen calibration data is not stored on an controller on the display panel? That would absolutely make sense.

[can16358p]

Can it be like:

Pencil also has a small calibration table and when paired with a new iPad it checks and downloads that immediately.

If not, it might also be (more likely) sending whatever it senses to iPad and iPad processes that raw input with the calibration data to determine the final output.