http://www.conti-online.com/generato..._ozone_en.html
mentions that a company called Bandage Inc has a card that 'grades' the cracking. I'll see if they have a downloadable version.
EDIT:
Sorry, I struck out. I can't find anything on that company & can't find anything on any gauges to determine severity of 'dry rot'.
On the funny side: I was helping a buddy of mine fix a tire on his (severely neglected) trailer. The dry rot was so bad that he had Fix-A-Flat coming out of the cracks. I was literally ROFL.
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