The preferred unit of measurement for datawindows on the screen is PowerBuilder Units (PBUs is the acronym). However for datawindows that are primarily to be printed, the preferred unit of measure is 1/1000 of an inch.
This aids in designing reports as you have better idea of where to layout objects. The screen corresponds to a real ruler.
Lines are drawn correctly vertically using 1/1000 of an inch, unlike PBUs. The vertical lines sometimes appear to have gaps when viewed in PBU mode.