A significant amount of interaction involves number entry. The purpose of any number entry interface is to accurately select or set a numeric value. There are two main styles of number entry interfaces found on medical devices: serial interfaces like the ubiquitous 12-key numeric keypad, and incremental interfaces that use a knob or a pair of keys to increase or decrease numbers. We report an experiment that investigates the effect of interface design on error detection in number entry. The initial findings show that the incremental interface produces more accurate inputs than the serial interface, and the magnitude of errors suggests that the incremental interface could reduce the death rate relative to the numeric keypad.