This is from the 2005 version of the Berkowitz-Cohen bridge notes. They retired in 2009. (There were later versions, but this is the latest available version for publication).
Warning: This is probably of use only to expert players who are in long-time regular partnerships.
ONLY PENALTY DOUBLES BELOW 2NT ARE IF:1) The opponents have already been “left in” or doubled for penalties (or we double Landy type, then double).
2) We open (non big-), our responder passes (their overcall or takeout double) and then doubles on next round-or 1M x xx sets up penalty X’s
3) We are in a GF (but not 1 open and no suits bid yet).
4) We open 2 or 2M and they overcall or we open 2 and respond 2 -- all X’s by either are pen.
5) We open, they overcall, our resp. passes, they advance 1 or 2NT, we pass, they pass, we X 1 or 2NT
6) Any place in our notes where double is specifically defined as PENALTY (Note: There are some scattered about other pages -- such as responder redoubles after our opening 1-bid.)
7) We respond 2/1 in competition and OPENER doubles
8) Our 1NT opener or overcaller doubles RHO’s call (regardless of our responder’s action) -- but not if RHO raised (or goes to suit shown by overcaller) (all x now takeout even by 1NT opener)9) Our third double in any kind of auction is penalty
10) We’ve bid 1 P 2.
11) Any time we have stopped (but not opened) in 1NT (...1NT-P-P) and they balance (X=2 or 3)
11a) Any time we have responded 1NT (in or out of comp) and then they bid a 3rd suit
11b) We open 1, respond 1NT: They overcall -- Double by either is penaltyWe open 1M, respond 1NT: They overcall -- Double by either takeout
11c) If we bid natural notrump over RHO’s suit, our notrumper’s later doubles are penalty even if the suit was raised. Partner of 1NT’er can never penalty double.
12) We dbl a suit that either of us have already bid naturally (but not of after our 1 opener)
13) We have a known 8+card fit and double (other than defined game-try double)--X=”xtras”14) Never penalty when we double their raise when in front of the overcaller.
Please send suggested changes or improvements to my office in Central Congo.