[Test-Equipment] Difference between PSM-45 and PSM-45A ??

[John Hensley]

A little more information:
On the back of the Fluke 27/FM that I purchased, the original Fluke ID labelsays it is a PSM-45.  The Army manual which came with it was labeled PSM-45A.This began my curiosity to see what I had.
I too found that the PSM-45 refers to both the Simpson 467 and the Fluke 27/FMand both as being True RMS meters.  There may be other manufacturers involved butI've found those two so far.  From what I've read so far both the Simpson 467 and theFluke 27/FM had to meet all the requirements of the PSM-45 specification to qualify andthat specification pretty much supported use on all military equipment except for onearea where operating temperatures dropped into the freezing cold climates.
According to Army TB 11-6625-3263-25:  
The AN/PSM-45A was procured to satisfy shortages of the AN/PSM-45. The AN/PSM-45A will not replace/purge the AN/PSM-45, it will be issued to users who require the AN/PSM-45. The AN/PSM-45 and the AN/PSM- 45A are functionally equivalent. The AN/PSM-45A can replace all items replaced by the AN/PSM-45.
and then to expand the mystery:
The AN/PSM-45B was procured to satisfy shortages of the AN/PSM-45A. The AN/PSM-45B will not replace/purge the AN/PSM-45A. The AN/PSM- 45B and AN/PSM-45A are functionally equivalent. The AN/PSM-45B can replace all items replaced by the AN/PSM-45A.
Technically so far I am very pleased.  I've gone around like a new school kid checkingreadings on different things and beginning to get some confidence in this meter.  My mainapplication for it is outside work where it has to tell me what is going on and in most casesI won't be able to tote anything larger.  According to Fluke it self-calibrates with the leadsshorted, auto-ranges from the highest (or safest initially available scale) to the scale needed,has a battery life of from 900 to 1200 hours, auto prompts when battery source is neardepletion, etc. etc.  
Anyway, what I have so far.  Semper Fi.