Meassurements on individual elements are WRONG

Hi (sorry I'm so frustrated), so the elements on a page ie. 20mm down and 20 mm in, from the upper left corner, is described in the toolbox by X: as 63,5 and by Y:126,5 - numbers that i have no clue what means. It is very disturbing for the flow of creation. I have worked with Adobe products since 1995.... Do you have any clue? Can you help me get the numbers match?

Thanx, Marina 🙂