First that letter was all about setting up a legal and public relations basis to question the election later.
Second, yes voting machines need calibration. Different types require different kinds.
For example the touchscreens, usually older resistive touch screens get mis calibrated on position. You have to remeber these things get locks in closets and sit in non-temperature controlled ware houses for a couple years at a time between elections, then they are jostled in trucks, cleaned with cleaners, and sometime run off various power sources. Empirically they do go out of calibration.
I personally have a ballot I saved from an AUtomark paper ballot printer in which all the votes are off by one oval width. that is 100% of the votes are incorrect and you can tell because a few are printed past the range of ovals.
Opscans are fairly easy to allign since they have relatively few degrees of freedom but they do get misalligned and become sensitive to printing tolerances.
Old lever machines used to have the gears wear down.
The solution to all this is not to require perfect everything but to have ways to check things. hand marked Paper ballots and some sampled recounts of those paper ballots such as is done in New Mexico is I believe the best compromise between transparency, robustness and simplicity. It's robust against human and machine errors so mere mortals can carry out very transparent elections. It's also robust against voter turnout variations too since it only takes more pencils to let more people vote, and if a machine breaks, you can still gather the ballots, so you dont get long lines at the polls.