There are three settings for the label printer, reached by the Label Printer Details entry in the AddressBook menu. This displays a dialog where the settings can be modified. At the top are a pair of checkboxes that set the units you are using for the various sizes. This may be set to mm or 1/72 in (points).
Note that no conversions are performed, changing the units will just change the labels and affect the values actually used in the printer settings but it does not change the values you put in. It only changes the units in which you are giving the values.The first setting is the paper size, this may be set in two ways, firstly by selecting one of the standard paper sizes from the drop down menu on the left, this will fill in the text fields with the correct values. The alternative is to enter the size directly into the text boxes, which must be done if the paper is not of one of the standard sizes.
Note that it is the value in the text boxes that is used, if you edit the value in the text field then you do not have to worry what value the drop down menu shows. The menu is just there as a convenient method of entering standard values.The second setting is paper margins. These are just entered into the boxes using the selected units.
The final setting is for the paper orientation, landscape or portrait.