Wanted to share another feature rarely used, the Mach4 DRO Auto Calc. I posted about it a while back, here.
One way to use it would be to touch a tool at the near edge, set X zero, move the tool and touch the far parallel edge - now you have the distance between the two edges. Using the DRO Auto Calc feature, you just divide by two! I’m not replicating it at the moment, but if I’m right that should put your X zero dead center of the piece, in that axis.
Repeat the process for Y. While those edges aren’t parallel on your counter top at least they’re equal angles with respect to the parallel ones. All you want is to find the mid-point, and this method can do that - within reason using a fluted tool or pretty darn accurate using a solid dowel. Since the machine’s motion can be limited to a single, accurate axis, you can basically trust its measurement when you know at least one work piece side is parallel to an axis.
You could also just use a handheld calculator, but that’s no fun - you have to type all the numbers in, and not fudge it up!