PPH,
I have never come across this abbreviation, and presume it is used only in specialised documentation, the (originally) exclusive readership of which would presumably have full knowledge of such various (and otherwise obscure) shorthand, probably only devised in the first place due to shortage of space on record cards or some such. Is this abbreviation exclusive to something like Air Ministry airframe record cards for instance? Could we have your guidance by providing some context here? This does sound like a case where guessing will not provide the answer with any guarantee of correctness.
David D
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