Abstract: A hot water distribution system for a dwelling or other building is designed to avoid the waste of water incident to letting the water run until hot water reaches an open hot water faucet or valve. Adjacent each hot water outlet valve there is a control unit having an inlet connected to a hot water supply line from the water heater, a supply outlet connected to the hot water faucet or valve and a return outlet connected by a return line to an inlet of the water heater. Between the inlet and the supply outlet of the control unit there is a normally closed valve which is thermostatically controlled so as to open only when water in the control unit is at or above a predetermined temperature. When a hot water faucet or valve is opened and water in the hot water supply line has cooled to a temperature below a predetermined value, the control valve remains closed and water in the hot water supply line is returned to the water heater by a circulating pump.

Abstract: A hand held calculator having a key board with numerical keys and function keys and a visual display is provided at one corner with a rotatable measuring wheel which projects beyond the perimeter of the calculator case so that it can be rolled along a selected line, for example a line on a building plan or map to measure the length of the line. Means is provided for sensing rotation of the wheel and generating a unit signal pulse for each increment of rotation of the wheel. These signal pulses are fed into the calculator circuitry as unit entries and are automatically added to obtain a total measurement entry representing the length of the line. Numerical keys and function keys of the calculator are thereupon manually operable so as to perform additional arithmetic operations on the measurement entry, for example multiplication or division.