What is a "Regulator" clock?

I've seen lots of clocks with the word "Regulator" printed or etched on the glass of the door covering the pendulum. What's the history of this name—is it a brand of clock or a type?
—Phil Hughes, Washington, D.C.

We turned your question over to one of the world's leading clock experts, Phil. Gregg Perry operates a studio in Pennsylvania (perrysclocks.com) specializing in the conservation and restoration of antique clocks and watches. He's also a certified appraiser of these timekeepers. Here's what we learned from Gregg:

Regulators were first developed in England around 1720. Typical clocks of the day were only accurate to within about 5 minutes per week. But regulators, such as the one shown at right, powered by a weighted and geared mechanism, could be accurate to within 10 seconds per month when properly adjusted. These clocks were initially used in observatories and clock and watch shops as the standard of accuracy during repairs, synchronization, and manufacturing.

By the mid-19th century, regulators were being mass-produced with high accuracy in Vienna, Austria. And near the end of that century, the American version of these clocks began to be produced in mass quantity with equal accuracy. The majority of these clocks kept time only, however, without any bells or chimes.

Regulators gained prominence in America in the late 1800s as the time standard in railroad stations of every town. Railroad employees would synchronize their pocket watches to these regulator clocks several times a day. This helped to reduce the number of train collisions.

By the 1920s, American manufacturers were displaying the word "Regulator" on the clocks' glass-front door as a testament to their heritage. But the name has always been a generic term to describe the type of clock, not a particular brand. And most modern clocks, such as the one shown above contain a quartz movement, with the pendulum simply for show.