Number entry is ubiquitous and there are several ways a number entry interface can be designed. Until recently, research has been focused mainly on one type of number entry interface: the numeric keypad. Various factors such as the range of values, and the space available for the design allows for several alternative interfaces to be used for number entry. In the design of medical devices such as those used for controlled drug delivery, accurate and timely entry of numbers are required in order to reduce any risk of harm to patients. This paper reviews five number entry interface styles and reports the result of an experiment conducted to evaluate the performance differences of the interfaces based on numbers used in infusion therapy in a hospital. The result shows a significant effect of interface style on speed and accuracy.