What is last number in screenshot file name?

[RedKnight]

I'm brand new to Action, so far it's great. Small question:

When you do a screenshot (F12), it saves a file of name e.g. "FTLGame 12-22-2014 11-18-00 AM-6.jpg". All this makes perfect sense except the number right at the end. It is not a sequential number; it bounces around.

I am looking for someone who *knows* what it is. No guesses or assumings, please. I already did that.

Thanks if you can help!