an electronic calculating device for conveniently calculating a percentage of a value , as is often performed in a restaurant or bar when calculating a gratuity based on the amount of a bill is provided . the invention is a device having a first side and a second side , with a control mechanism on the first side which the server or diner can use to input a bill amount . a control mechanism is positioned on the second side for causing a processor to calculate a percentage value of the bill amount . preferably , a display is provided for displaying the percentage value or tip amount , as well as the total of the tip and the amount of the bill .