I was trying to print business cards from InDesign to an HP 2510 (non-postscript) printer. I created 10 boxes (two columns of five cards each). The result was measurably off - what was set up to print in a space 7"x10" prints to a much larger space.

As an experiment, I created a single box of that size, centered on an 8.5x11" page. The resulting box, instead of 7"x10" measures about 7-3/8"x10-3/8". What on earth?

Does anyone know what is going on? I know that the printer understands inches (or postscript picas, for that matter) because I can do this correctly from MS Word.