[Chimera-users] automated selection of most N-terminal residue in model

Hi, I'm trying to measure the distance between the N-termini (or the first known residue) of a batch of dimeric proteins. The two proteins are different chains. I know how to do this by hand, but am exploring different ways to script it. It may be best to avoid using chimera entirely, but I thought I'd check to see if anyone knows a clever way to select the residue closest to the N-terminus when it's not residue #1. Thanks for your help. Michel