I use three letter codes often and have for years. I guess I pretty much made up my own on the ones that weren't obvious and have been treating those as if they are the universal standard ... because of course they should be. NYM, PHI, ATL, WAS, MIA CHC, PIT, MIL, StL*, CIN LAD, SFG, SDP, ARZ, COL NYY (when not using MFY), BOS, TOR, TBR, BAL CHW, CLE, KCR, DET, MIN TEX, HOU, LAA, SEA, OAK * And, yes, I usually take the trouble to use the lower case t