The Ives Catalog has a chart referencing what Opening Width range each size coordinator could be used on and common applications of equal pairs of doors.
To determine the size COR you need;
In the case of an equal pair of 36" door (X = 36" and Y = 36");
INFORMATION PROVIDED THROUGH THIS SITE IS PROVIDED TO YOU AS IS WITHOUT ANY EXPRESS REPRESENTATIONS OR WARRANTIES OF ANY KIND, AND WE MAKE NO REPRESENTATION OR WARRANTY THAT THIS SITE(OR ANY INFORMATION PROVIDED IN RESPONSE TO YOUR INQUIRY), WILL BE ACCURATE, COMPLETE, OR ERROR-FREE.
YOU AGREE THAT YOU MUST EVALUATE ALL INFORMATION AND RESPONSES, AND THAT YOU BEAR ALL RISKS ASSOCIATED WITH, THE USE OF THIS SITE, INCLUDING ANY RELIANCE ON THE ACCURACY,COMPLETENESS, OR USEFULNESS OF ANY INFORMATION OR MATERIALS MADE AVAILABLE THROUGH THIS SITE.