For linear delta printers like the Kossel mini, the positional accuracy (assuming perfect mechanics and motors) isn’t the same uniform grid as on a cartesian printer.
The graph above shows the Z error when rounding the actuator (linear rail car) positions to the nearest 1mm on a printer the size/dimensions of a Kossel mini. Near the center there’s less error (more white), and near the towers you can see strong red/blue rings where that tower’s rounding is more prominent in the position of the effector (the part your hotend is mounted to).
In the same way that whosawhatsits microstepping calibration test shows rounding on a cartesian printer, I’m sure there’s a mechanical way to see these rounding problems on a print. Maybe just a 6 point asterisk pointing towards and away from towers would show them.
Just thought that was a neat thing to graph.