As you probably know, buttons and hotspots have different key types (set, momentary, toggle, change page, etc). Well, one of them is CalibrateTouch or something like that. Almost every B&R HMI I've done for the past 12 years has had a splash screen with a big hotspot on it somewhere that starts calibration that way.
The slightly better way to handle this is by using a spare digital input to trigger one through the VisAPI library. That keeps malicious operators from jacking up the calibration on purpose to force some down time.
The little button on the settings page of all the demos is useless. If the calibration actually goes off, it would be a pain to navigate to and press that button.