Thanks everyone - seems like the first guess was correct. I'll pass the details on.
4PON4PIN
Enough of the puns - not Montag, I'm watch and clocking all day - talk to you on Tuesday.
John T - I think that 4Ps may be correct, since the Honeywell response indicates that the reference is to an engineering based calculation. Anyway, they say that it should not have been included in the handbook so the relevance is decidedly less.
Again thanks to all.