X mode and Z mode are used to gather readings from your POS regarding your total figures and sales.
Both modes can be accessed by pressing the home mode button then pressing the end of day button on the home mode screen.
The main differences between the two modes are that the X mode reading can be performed multiple times throughout the day without affect your totals.
A Z mode reading, once performed, will reset your totals for that day. So this mode reading should only be used at the end of the day. Using this mode will prompt if you would like reset your totals before doing so for peace of mind.