Horstmann E7 Quartz is an electro-mechanical water heating control that can be set to take advantage of cheap night-rate electricity, so that there is a tank of hot water available for the morning.

The device has a 24-hour dial that rotates once each day. It can be set to the "WINTER TIME" or "SUMMER TIME" line, depending on the season. The clock is adjusted by turning the dial clockwise. A battery reserve will keep the clock running even if the mains supply is interrupted for up to 6 days.

The device has a water heater switch that can be set to the "OFF", "TIMED", or "BOOST" position.