A subterranean drilling system may include a drill string and a rotary drill bit coupled to the drill string. A plurality of sheet inverter fingers, each with a friction enhancing surface on a free end, are interdigitated between the belts of the sheet stacker. The radiation therapy device includes an x-ray source for diagnostic x-rays and an x-ray detector of the diagnostic x-rays. The first and second transmission power levels are governed using closed loop power control such that transmission power level is controlled to achieve a required quality of reception parameter at the receiving end of the link. One embodiment of the fitting also comprises a glass fiber reinforcing member that provides structural strength to the fitting member. The functionality provided to the electronic devices by such a first-level removable module can thus be provided in part by the application specific circuitry within the removable module and further in part by the type of external IO of the second-level removable module.