the idea of holey calibration (make a grid of holes, measure them and correct accordingly) is a very good one, and done well produces good results.
The problem is in accurately measuring and then repeating the process.
So I would like to have people think about flipping the process.
First create some lines on a workpiece (very easy to do accurately with a square running along the edge with a pencil on the other end)
Second, tell the system where the lines are.
Third, put a pointy bit (v-groove or just very tiny bit) in the router
Fourth, manually drive the router to each position and click to tell the system which point you are on (allow points to be defined and redefined in any order)
Fifth, have the system crunch the numbers and calculate the correction values.
Sixth, have the system drive to each point and have the person indicate that it’s correct, or if not, drive to correct the position (ideally this would be a different point than the first ones, further out or closer in to check if the calibration holds across a larger area)
loop though this until the person is satisfied.
The system can measure the chain position with very high accuracy, and I think putting the point of a v-bit on a crosshair of lines can be done far more accurately than trying to measure the distance between holes with a tape measure that’s (at best) marked in mm, with precision questions on the tape measure accuracy.
I would also change the default chain length so that instead of being a fixed 1651mm it extends the chains to the 1651mm length for you to hook the sled to, and then lets you drop the sled by one tooth at a time until it gets to the point that you consider the ‘center’ of your workspace (at that point, it should be within about 1/4" of the true center of the workpiece, but that is an easy 0,0 to mark and to drive back to.