Need Help With Unique Numbers

[carmuse]

I'm hoping to get some help on something I've been working on for several days and have not been able to figure out! I'm designing a database (I'm a newbie) for a High School Honors Band Audition. I'm working on the front end and trying to get filemaker to assign audition numbers to each student based on the instrument they are auditioning on. So flutes would be A(x) piccolos would be B(x) etc. for all 23 different instruments that we are auditioning that day. Each number has to be unique and they all should start at 1 and go up to the total number of people auditioning on each instrument with no gaps in between numbers. I've got it worked out so that when I enter the instrument into the database it auto enters the letter prefix but I can't get the number to increment. I'm using Serial Increment and have read all the posts about this to get it to increment but I can't get it to work. I'm close to giving up and just entering in the audition numbers by hand but figured their has to be a way to do it with a script or calculation or both. Any help would be greatly appreciated!

[comment]

Perhaps this might help:

http://fmforums.com/forum/showtopic.php?tid/199115/post/307990/#307990