There's no need to change the number of decimal points, which tends to mess up the UI slightly.
Just type in your page size to 3 decimal places, and the same for any other object. Xara retains the size to 3 decimal places but rounds it to 2 in the display boxes only.
Here's an attachment that if you export as svg and reopen in inkscape shows the correct sizes are maintained as 3 decimal places. Perhaps someone can try to see if it's the same as a pdf export,. I can't see this information in Adobe Reader.
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