Non-Round Diameter: Widest Possible? [Risolto]

When measuring coins that are not round -- for instance square-ish coins, do we go from corner to corner, to get the largest possible diameter? Or do we go from the middle of opposite sides, to get the smallest possible diameter?

I'm guessing largest possible, because for instance, with scalloped coins, it's also possible to measure two different ways, but I'm guessing that with scalloped coins, it's automatic to get the widest possible diameter.

Is this guideline documented anywhere in Numista?

We have the Guidelines... in the Numisdoc section. There you can find all about diameter.

https://en.numista.com/catalogue/contributions/instructions.php

Guidelines say to measure the largest diameter, but in the catalogue sometimes a smaller diameter is given, for example, here (Egypt, 2 Qirsh - Farouk, 1363 (1944)): https://en.numista.com/catalogue/pieces8677.html
Maybe the figure was simply copied from a source without any measurements done?

Hello,

 

Rectangle, square and oval coins can now have their size in 2 dimensions.

 

For other coins, the guidelines mention that we should specify “the largest spatial dimension”. For regular hexagons, it means the distance from one angle to the opposite angle. See https://en.numista.com/catalogue/contributions/instructions.php#diameter.