A circular slide rule used to relate water flow rate, temperature differential and power for large electron tube cooling circuits. By measuring two of the parameters, the third could be calculated using this 12.5 cm circular slide-rule. For example, knowing the water flow rate and the temperature difference between the input water and the exit water, the power being deposited in the device can be quickly determined. This calculator, made of card stock, was produced by the Raytheon Company, a manufacturer of high-power electron tubes and that had a power range up to 10 kW. It was used at the Commercial Products Division of AECL in Kanata.
