I'm working on a WordPress plugin to manage rock climbing data, and I need to think of a way to store rock climbing grades from all of the different systems in a unified way. There are many different systems, all of which have some numerical system.

A comparison of all the systems: http://en.wikipedia.org/wiki/Grade_(climbing)#Comparison_tables

Is there some unified way that I can store and analyze these, or do I just need to assign numbers to them all and call it a day? My current plan is to save the score type and then assign each score a numerical value, which I can then use to compare and graph them.