indefinite articles - Does one use 'a' or 'an' before the word X-Ray?

I was asking this question on Area 51: "How do I tell if an airport scanner is a X-ray scanner?", but I keep wanting to put an 'an' in front of X-ray because it starts with the 'eh' sound.

So is it 'a' or 'an'?

Answer

Definitely "an". The word X-ray is never pronounced any way other than "exray", and as has been discussed before, the choice of a or an is based solely on pronunciation, regardless of spelling. Since X-ray is pronounced beginning with a vowel, it must be preceded by an.