In places where work must be conducted according to precise schedules, such as in communication, industry, and schools, clocks showing the correct time in multiple locations within the facility are required.

The best method to achieve this is offered by the electric impulse clock system. The first master clocks were invented around 1839-1840 by Steinheil in Germany and Wheatstone in England. The most common brands used by SJ were LME-Siemens-Westerstrand and Indukta.

As master clocks at SJ, pendulum clocks with weight or relay drive were commonly used, equipped with an impulse generator that emitted polarity-changing impulses to secondary clocks. Impulses were emitted every half-minute.

In the late 1960s and until 1980, all pendulum clocks were replaced with electronic clocks. The first ones were constructed with so-called discrete components (transistor, capacitor, and resistor).

Time was controlled by a crystal swinging at about two million cycles per second. Later, discrete components were replaced with integrated circuits, allowing for the inclusion of all holidays and the programming of daylight-saving time 25-30 years into the future.