The Plural of RPM

[tom.green at iwon.com]

I'm having a back-and-forth with an engineer about how to write more than one RPM. She wants to write, "RPM's." I freaked and said, "No, that would be saying, it's the Rotation Per Minute's problem." 
I know, it doesn't make sense.
I want to simply write RPM, meaning Rotations Per Minute. 

Am I correct or is there another way?

I also hate to apply the possessive to an inanimate object or a company for example, "IBM's net worth." Is there a rule about that, or is that just me?


































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