I'm running 24" / 61cm paper rolls on a HP Z3100 and setting the paper size on the printer on Super D/A1 format, that is 610 x 914 mm. Calculating the 5 mm border at left and right side at the Z3100 I should end up with a useable width of 600 mm.

Opening Qimage I get a useable paper size of 599,6 x 904,4 mm. But looking at the Print Properties Qimage says 600 x 904 mm. Why?

Next thing: Setting up a print size of 200 x 300 mm, two prints doesn't get aligned horizontally because of the missing 0,4 mm.
If I specify a print size of 200 x 299,8 mm, the prints get aligned. Now comes the curious thing: I close and reopen Qimage and the same print size of 200 x 299,8 mm specified before is rounded up to 200 x 300 mm, and the prints are aligned horizontally as before.

That freaky little distance of 0,4 mm seems to float around somewhere between the program lines of Qimage...