The present invention provides a method and apparatus for determining a retail performance metric of entry identification time. A base clamping mechanism is affixed to the computing device. A movable jaw is slidably supported on the body portion such that the movable jaw can move relative to the fixed jaw to vary the spacing between the jaws. The process dependent element may be a diode connected transistor, for example. The measured traffic rate is compared with a committed rate to determine if the measured traffic rate exceeds the committed rate.