In the early days, mechanical clocks didn't boast an impressive level of precision — they didn’t even offer a decent level of precision.

 

Truth be told, the mechanical clock left much to be desired in terms of timekeeping accuracy. But it had two advantages over the comparably far more accurate sundial, which made people consider mechanical clocks as an alternative to sundials.

 

The first advantage was that they could tell the time at any moment, even when the most accurate of sundials wouldn't be of any use, such as when the sky is overcast or at night. The second advantage mechanical clocks had was that they could do more than just tell the time.

 

They could also chime the time with bells or gongs if equipped with the right complication. Moreover, clockwork mechanics paved the way for the invention of many more additional mechanisms and functions, some of which were practical while others were created for fun.

 

A 16th-century portable drum watch with sundial (Credit: Wikipedia)
A 16th-century portable drum watch with sundial (Credit: Wikipedia)
An early watch from around 1505 purportedly by Peter Henlein (Credit: Wikipedia)
An early watch from around 1505 purportedly by Peter Henlein (Credit: Wikipedia)

Mechanical clocks could finally be brought inside, which made a big difference on cold winter days. When it came to timekeeping accuracy, it's worth mentioning that early mechanical clocks had one key problematic component — their escapement.

 

The invention of the first escapement led to the development of the first all-mechanical clocks in the 13th century. The verge escapement was used everywhere up until the mid-19th century, which worked in tandem with a primitive balance called a foliot.

 

The foliot was like a carrying pole. Clocks had regulating weights near its ends affixed to a vertical bar called the verge, which allowed the clock movement rate to be adjusted somewhat by moving the weights in or out on the foliot.

 

 

The first escapement inventioned in the 13th century was the verge escapement.

Yet this still only ensured accurate timekeeping to around one hour at best. That's why sundials were always consulted to correct the time on these clocks, or else they went by the movement of the stars in the night sky (astronomical tables had to be consulted to do so). The first personal and portable clocks were even less accurate.

 

Clocks constructed in the early days of mechanical watchmaking — predominantly tower clocks —  had a falling weight to ensure a smooth transfer of energy to the escapement mechanism. It was adjusted for mechanical parts with shapes and surfaces that were far from ideal.

 

The spring-driven movement was invented after the weight-driven movement. It dates back to 1410 and is believed to have been introduced to clockwork by the Italian architect Filippo Brunelleschi. Springs made it possible to create timepieces that could be carried around, although there was a price to pay for this.

The tension of the spring would be at its greatest when the clock was fully wound, and this tension would fall at an uneven rate as it unwound. That's why owners of early portable clocks could only expect the timepiece to be accurate to the nearest few hours at best.

 

The fusee helped rectify the situation, which is believed to have been first used around the time when clockmakers began using mainsprings in spring-powered clocks in the early 15th century. A fusee is a truncated cone or a spiral-grooved pulley onto which a chain or cord is wound. The free end of the chain is attached to the mainspring barrel.

 

When the mainspring is wound in the barrel, the entire chain is wrapped around the inner "spindle", and begins to unwind from its smallest part at the top. As the mainspring runs down to the bottom, the chain going to the barrel comes off wider and wider grooves on the fusee, which increases torque according to the lever principle.

 

Verge and foliot
Verge and foliot
Fusee
Fusee

This doesn't contradict the law of conservation of energy, as the mainspring barrel's pull increases proportionately. An alternative to the fusee called the stackfreed was invented in southern Germany in the 16th century.

 

It's a spring-loaded cam mechanism with a roller at the end of the spring arm, which presses against an eccentric cam mounted on the mainspring arbor. The inconstant driving force (torque) and equalizing retarding force exerted by the spring arm on the cam was used to reduce the mainspring's torque as it unwinds.

 

 

An alternative to the fusee called the stackfreed was invented in southern Germany in the 16th century.

The fusee was a more effective mechanism for equalizing the uneven pull of the mainspring, but the retarding spring arm had the advantage of being more compact. Watchmakers had built up a wealth of experience working with movements by the mid-17th century, towards the time when the groundbreaking inventions of balance springs and wheels were made.

 

Well-adjusted clock movements with verge escapements and fusees could easily boast daily losses and gains of just around five minutes by around that time. The ordinary deviation was fifteen minutes, and deviation in third-rate clocks or ones that were worse for wear reached up to thirty minutes.

 

Ancient German watch movement with stackfreed
Ancient German watch movement with stackfreed
Jost Bürgi
Jost Bürgi

The most technologically advanced timepieces by the Swiss watchmaker and mathematician Jost Bürgi were equipped with the cross-beat escapement and remontoir d’égalité he invented. He managed to bring the daily losses and gains down to less than one minute, which allowed him to put a second hand on his clocks. He was 100–150 years ahead of his time, when the second hand became standard.