The printer is calibrated during the connection process, when you tap Add Printer and print a test page. If you cannot see some of the markers on the test page, you need to change the values of the calibration markers accordingly. These changes will apply to the next document you print (the calibration page will remain the same).
To adjust the margins and calibrate the printer for the different page size, please do the following:
Note: This option is available for Bonjour printer only. There is no need to calibrate printers connected via Printer Pro Desktop, as in this case calibration options are set by your printer driver on a desktop computer.