Some alarm clocks can set multiple alarms. Digital alarm clocks can make other noises. Products include branded digital cameras, alarm clocks and other electronics. Button cells are commonly used in electric watches, clocks, and timers. The anchor became the standard escapement used in pendulum clocks. It was measured with sundials and water clocks. It was also used for springs, including those used in clocks and watches. Excise taxes were added on luxury imports such as automobiles, clocks and watches. The chime tune used in almost all longcase clocks is Westminster Quarters. These early water clocks were calibrated with a sundial. In 1665 Huygens made a curious observation about pendulum clocks. The master periodically broadcasts the current time as a message to the other clocks. Notations about the time on the clocks can be made. His work demonstrated the existence of endogenous (internal) biological clocks, which synchronize biological rhythms. The second became accurately measurable with the development of mechanical clocks.