This is a fantastic trick!!! You can use it in a show, in a restaurant, bar, with friends. Imagine the following: You borrow a 1 dollar bill from some one, and fold it 4 times, and ask the person to hold it in a fist.first . Next you show a normal calculator, and show that it makes all functions. Hand it to a spectator and ask him to digit the year he was born. Multiply by the day he was born. Divide by his wife age. and some more calculations as you like, and numbers chosen by the spectator, random. Next, you ask her to calculate 22 percent of that number, by pressing X , 22, %.