If a employee is in charge of adding money what do you do when they come up short?

I'm not sure that I understand your question, but what it seems to be saying is that a person is adding up money from something and his totals don't agree with what should be there.  If that is true, i.e. if it's money in a cash drawer that used to take in and dispense money, there could have been a mistake made in giving out change so the register wouldnt agree with the tapes if there are any.  What exactly are you using to come up with the fact that he is short?

Recount, if the problem has not resolved itself, then the next step is to relocate the employee.