Hi, I decided to pay $500 for PC-SPAN, so I can better understand the margin requirements for my future options account (primarily trading NYBOT/CME). I'm just not sure how to figure out which parameter files I need to be using. I'm looking here: ftp://ftp.cmegroup.com/pub/span/data/cme/ What's the naming convention here? 'a'? 'c'? 'e'? 'i'? Help?