Developer density in an electrophotographic system is measured. An apparatus can process an item of produce having a first portion and a second portion attached to the first portion. The method includes forming a second material layer over the first material layer. The sheets are compressed to both bind them together into a stack and create axiallongitudinal undulations. The adjustable body bias circuitry can produce an adjustable negative body bias voltage for biasing n-channel metal-oxide-semiconductor transistors.