I just downloaded Joystester 2 (thanks for the link BTW).
Bloody hell! My old analogue pot X45 is better than either the X52 or X52 Pro if obtaining ever increasing but tight circles is the benchmark. I just put my X45 up for sale on Ebay but me thinks I might sell one of the X52's
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The X52 Pro does have a better resolution than the X52 but both give diamond shapes. Modded X52 = No difference other than improved sensitivity from centre.