X and Y not quite matching up

I have a tray that I’m milling and the outside walls are uniform thickness.
When I mill it the two short walls on the outside come out thinner by almost a whole 1/16th of an inch.

I generated this as an SVG in illustrator and measured it, In that file I have the same wall thickness.

I don’t know when this problem started, but I’m a bit curious if its correlated to adjusting my potentiometers?
I switched to GT3 belting a bit ago and had to turn my motors up a hair to keep them from locking up. (I think mine were set a bit lower than average from the factory as they were barely turned on, and I was having jamming problems all the time when I was on GT2 Belting anyways)

So I just cut a 8" by 8" square and it comes out to 8 on the Y axis but only 7 7/8th’s on the X axis.

So I converted the inches to MM and then did this calc.
203.2 / 200.03 = 1.01584762
26.667 x 1.01584762 =27.0896

203.2 is 8" 200.03 is 7 7/8th’s
26.667 is my current $100 settings in my GBRL driver (I have GT3 belting)
I multiplied it by the 1.015 factor and then changed the $100 setting…

This worked and now my square is actually square. however I feel like this might be a band-aid for a different problem.
Or is this just how one calibrates a machine?

You will end up needing to do that on all three axis. See this video for more information on how to do a complete calibration.

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Sweet. looks like I’m on the right path then!