This is a great version of a utility item.
The calculator appears normal in the hands of the spectator.
Your force number can be easily set even in front of the spectators it is that simple.
Once your force number has been shown the calculator acts completely normally so you can leave it with the spectator to check that there is no funny business.
Imagine that you ask a member of the audience to join you on stage and help, they are passed a calculator and as random members of the audience call out number they total these. After a few spectators have called out numbers the total is checked and it happens to be the date of the show, or a number that you have predicted, or 666, or anything else that you like.
Each pack contains a pocket style calculator, instructions on how to program any force number, and a suggested routine. This one though is only really limited by your imagination for what you can do with it.