@CaptainBohemian The reason I consider it obvious is that in my experience, it's a pretty commonplace abbreviation even among nonspecialists to my recollection. It's an abbreviation you might see on television shows like
Jeopardy for instance. I'd be willing to bet that it's the most common abbreviation on the list by far, (although naturally P.I.E. would rank higher in an ngram due to false positives).