Print Scale Problem: Wenatchee 5 Build 2014-10-14

I was attempting to print at a 1:1 scale and my print was coming out too large. I measured and made a scale adjustment (seems to be 0.966 scaling factor) and can print so an inch is an inch. Is this related to the display resolution difference on Mac vs Windows machines? Is it a bug?

This is an inaccuracy in your printer. The scale adjustment is provided so you can make adjustments like this.

I will have to second Michael on this. I was only too happy that printing to scale became possible in Rhino, so I made some prints of my design in a 1:1 scale on a previous version (some 4 weeks ago, don’t know the version number anymore).
I just checked these prints again, and they are accurate to at least 98%, possibly better.
Now (version 5A552) I am printing a line of 250 mm length and it comes out as 233 mm, which is almost a 7% error! Same printer, same Mac.