Hey John,
I would consider 1/32" (~0.8 mm) as not as accurate as could be possible, and I think it could already make problems with tiling.
Even if you use a geometrical method (the special case of the Pythagoran theorem known as 3-4-5), you don’t really use a geometrical method since you use the tape measure as reference object (difference between comparison to a reference object and geometrical method).
Why not use a purely geometrical method (comparing diagonals) like the bar gauge method? Here you are not limited to the accuracy of a measuring instrument.
The best test is of course milling something (a rectangle on a workpiece of workarea size with the tip of a V-bit) and then check this with the bar gauge, or: Try if you mill the same lines after rotating the workpiece by 90° (or if on the result two lines have an angle to the previously milled lines then, then it’s not square)