Computer auxiliary gear box

For use with a mechanical fuel pump computer having a variator and a register wherein the variator has an input shaft normally driven by a fuel meter in accordance with the volume of fuel delivered and is settable to establish a selected unit volume fuel price and wherein the register has a resettable volume counter drivingly connected to the meter via the variator to reflect total volume of each fuel delivery and a resettable cost counter connected to be driven by the meter via the variator in accordance with its setting to provide a price readout of the total cost of each fuel delivery, a converter usable for expanding the price range of the computer and for setting the computer to compute and register total volume and cost of each fuel delivery based on a price for a first unit volume and alternatively for another unit of reduced volume, the converter comprising a converter housing attachable to an underside of the variator, a meter driven rotary input and a rotary output, the rotary output including a variator drive gear, a selectively settable drive connection between the rotary input and the variator drive gear for driving the rotary output at a first drive ratio setting from the rotary input to the variator drive gear for computation and registration of fuel deliveries in preselected units of volume and alternatively at a second drive ratio setting for computation and registration of fuel deliveries in units of different volume from that established in said first setting, and an interlock movable from a first operating position to a second operating position to change the drive ratio from said first setting to said second setting, the interlock extending outside the housing in said first operating position, and means inside the housing engageable with the interlock in said second operating position to positively prevent return movement thereof to said first operating position.