I have recently acquired a very secondhand S-wave (7S26-0110) which is missing its crystal and seconds/sweep hand. I figured that I could replace the crystal with one from CousinsUK because the oem one (310P03HN03) appears to be discontinued. Measuring the diameter with the crystal gasket in place yields a measurement of 30.75mm approx. Is it possible to infer the original crystal diameter from this measurement? When I swapped out a turtle crystal, the crystal gasket was about 0.6mm bigger (outer edge) than the crystal diameter tapering to about 0.2mm smaller than the crystal (chapter ring edge). Anyone have any suggestions what size I should order?