When you press the "Print" button briefly, the currently-set exposure time is stored. This stored time is subtracted from the set time when you press-and-hold "Print" to give you the burn-in time. It is stored until the next short press of "Print" at which point the stored time is updated, so you can make as many burn-in exposures as you like.
Calibration of exposure does indeed introduce an offset or correction factor to the basic settings, just as you might calibrate a camera exposure meter to get the results you want. Contrast calibration is done in ISO(R) units; if your paper data sheet specifies contrast in ISO(R) units you can enter those figures into the Analyser unchanged as a starting point, though I'd still recommend doing a full calibration for best results.