Why do all of the OSR games I’ve looked at insist on sticking with descending armor values? Ascending armor value is an easy and intuitive change. It just makes sense in a system where you roll a d20 versus a target number to hit. This is the best thing to come out of third edition, in my opinion. Is this insistence on descending armor class mainly a compatibility concern, aimed at keeping the rules consistent with previously published material? I have to assume this is the reason, but I don’t know if it’s a good enough reason. Most old school gamers love charts and tables, and a couple of “AC Conversion Charts” would straighten out the compatibility issues. Anyone who can calculate the THAC0 of a 9th level cleric in their head can figure out how to change AC 4 to 15 on the fly.