Our office issues Take a number tickets to customers when they are waiting to
be called-served. Hundreds each business day.
These paper tickets are premade, currently with each roll starting with
ticket #A00 and ending with ticket #J99. (why they don't go to the letter "Z"
is a mystery anyway)

I've got an excel sheet that a staff employee enters hourly the current take
a ticket number pulled and the current take a ticket number being served for
statistics.

I want a formula that compares these 2 data entries and counts how many take
a ticket numbers have yet to be served at that time (how many customers are
waiting to be served).
But since the tickets numbers contain a letter, I'm having trouble coming up
with a formula.
Thanks for any help!