1bu = 1cm works for me.  But don't forget,  the measurements grid goes to 3 decimal points although you can't see more than 2.
in other words..............20.48 could be adjusted to 20.485 but you wouldn't see the '5' on the grid.

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All the Woes of a World by Jonathan Icknield aka The Bryster

And in my final hours - I would cling rather to the tattooed hand of kindness - than the unblemished hand of hate...