An electric clock is a clock that is powered by electricity, as opposed to a mechanical clock which is powered by a hanging weight or a mainspring. The term is often applied to the electrically powered mechanical clocks that were used before quartz clocks were introduced in the 1980s. The first experimental electric clocks were constructed around the 1840s, but they were not widely manufactured until mains electric power became available in the 1890s. In the 1930s, the synchronous electric clock replaced mechanical clocks as the most widely used type of clock. Electric clocks can operate by several different types of mechanism: Electromechanical clocks have a traditional mechanical movement, which keeps time with an oscillating pendulum or balance wheel powered through a gear train by a mainspring, but use electricity to rewind the mainspring with an electric motor or electromagnet. This mechanism is found mostly in antique clocks. Electric remontoire clocks have gear trains turned by a small spring or weighted lever, called a remontoire, which was wound up more frequently by an electric motor or electromagnet. This mechanism was more accurate than a mainspring, because the frequent winding averaged out variations in the clock's rate caused by the varying force of the spring as it unwound. It was used in precision pendulum clocks, and in automotive clocks until the 1970s. Electromagnetic clocks keep time with a pendulum or balance wheel, but the pulses to keep it going are not provided by a mechanical movement and escapement linkage, but by magnetic force from an electromagnet (solenoid). This was the mechanism used in the first electric clocks, and is found in antique electric pendulum clocks. It is also found in a few modern decorative mantel and desk clocks. Synchronous clocks rely on the 50 or 60 Hz utility frequency of the AC electric power grid as a timing source, by driving the clock gears with a synchronous motor. They essentially count cycles of the power supply.