A timing system is described which provides sharp, one‐millisecond, electric pulses at one‐second intervals. These pulses are used to actuate a trigger circuit which is used to control one or more relays. The accuracy of the time scale can easily be checked against radio station WWV. Auxiliary apparatus can be controlled for time intervals of any even number of seconds. The accuracy of this interval can be determined to better than one millisecond. This system has proved to be particularly useful in calorimetry.