articles - We are physicists and we are arguing over the use of "a" and "an"

Here is the situation. I am in an office full of physicists and one physicist is writing his PhD Thesis. Fundamentally, he wants to know whether he should type "an SV" or "a SV" into the computer.

SV is an acronym for "Secondary Vertex", so it is clear to us that "a secondary vertex" is correct.

So the argument is over whether

• a or an "sounds better"

and additionally

• is SV a new, alternative word which means the same thing as "secondary vertex" (just as one can use "roll", "bap", "barm" interchangeably in the phrase "bacon roll" to mean some bread which is probably also buttered into which one has inserted some grilled, or otherwise cooked using another method, bacon causing the butter to melt into a delicious snack most suited for eating at lunchtime.




• or is SV an object which is to be expanded by the readed using a previously defined definition (should one read "SV" as "secondary vertex"?)

So, he should type "a secondary vertex", but is it "an SV" or "a SV". My vote is for the former as it "sounds better". (Or at least that is my opinion.)

Finally, we also consider "an STFC" or "an SRVTLVF" to be "better sounding", however "a TRVTLVF" seems to be "better sounding". We have discovered that it doesn't seem to matter what the letters of an acronym following a first "S" letter are, the "better sounding" choice is still "an" rather than "a".

Is there a rule about whether "a" or "an" should be used for acronyms?