Accuracy of Automatic Watches

Precision in timekeeping is of utmost importance to everyone relying on his or her wristwatch to tell time accurately.  Not all timepieces offer the same accuracy and there is a marked difference between a quartz watch and an automatic watch. Here we take a look at the standard accuracy of automatic watches and of quartz watches, as well as at the factors that can affect accuracy in automatic watches.

Mechanical watches are comprised of many components that range from small gears to bridges, levers, springs and screws – all of which must work together in unison like a carefully orchestrated dance.  As they interact, those tiny components power the watch and keep the energy flowing in order to stay accurate.

In a standard mechanical automatic watch, timekeeping can deviate by as much as plus or minus (+/-) 10 seconds a day. Typically, mechanical watches can accurate to within +/- 5  seconds a day While the accuracy of mechanical watches can be as high as +/- 3 seconds a day. Watches with a mechanical movement that have been tested and certified as a chronometer will retain an accuracy of -4/+6 seconds a day. The accuracy rate presented to automatic watches is typically an average rate over a few days.

The accuracy of mechanical watches can vary day by day, depending on several factors, including the position of the watch, movements of your arm, as well as the temperature or environment. All watches tend to gain or lose a few seconds over a period time, but let’s take a look at specific factors that can influence the movement.

The accuracy of mechanical watches can be affected by the position of the watch when it is not being worn on the wrist. Most mechanical watches are affected by the forces of gravity when they are in certain positions. Generally, the balance wheel inside has been adjusted by hand to compensate for losses and gains of time when the watch is in certain positions when worn all day. Watches are adjusted for anywhere from two to eight positions depending on the type of movement. Those positions include the dial side up, crown down (as if you put your watch on the night stand on its case side resting on the crown), dial side down, and a few other positions. Depending on the position the watch is placed in when taken off at night, for instance, may vary.

Temperature can also affect a watch because the parts inside expand and contract in extreme heat and cold – taking a toll on the balance wheel. In an effort to combat the effects of extreme temperatures, brands have turned to high-tech materials and designs that can compensate for temperature change and still maintain accuracy.

Typically, a watch placed under high temperatures tends to lose time, while watches placed under low temperatures tend to gain time.

Mechanical movements can be affected by magnetic fields. It is important to not leave a watch close to magnetic objects for extended periods of time.

The movement within a watch consists of many tiny steel components. When a watch encounters a magnetic field, the magnetic charge can pull these pieces in different directions, potentially slowing down cogs or bringing them to a stop.

The balance spring is the heart of an automatic movement and is typically the cause for concern when a watch is exposed to a magnetic field. The balance spring is a tiny, delicate coiled spring that causes the wheel to pulse back and forth at a certain rate of beats per hour, considered the “heart beat” of the movement. The energy from this spring is then dispersed throughout the movement to move the watch hands and power any complications. The magnetic field can come into play by potentially shortening its swings, and therefore speeding up the frequency.

Forceful shocks to automatic watches can affect the components of the mechanical movements. It is recommend to remove your watch before playing impact sports as to avoid direct strong impacts.

In comparison to magnetic fields, shock can also disrupt the balance spring as it is constantly in motion at a fairly high speed compared to other components. When a watch receives a shock, the heartbeat of the balance wheel can be disrupted. 

Over time, mechanical movements can begin to vary in accuracy. As the watch gets older, the lubricants and oils inside can start to break down and, like a car, when that happens, the levers and gears don’t interact as smoothly as they used to – possibly causing a slight inaccuracy increase. This is a normal occurrence after several years, which is why it is recommended to have your watch serviced approximately every five years to maintain accuracy.

Through innovations and new materials, watches can protect itself from certain levels of shock resistance, magnetic fields, and extreme temperatures. Movements containing a silicon balance spring, also known as silicium, are antimagnetic and offers enhanced stability to temperature variations. It allows for a higher level of accurate timekeeping due to its increased rate of stability. Collections like the Longines Spirit, Record, and various other models all use a silicon balance spring within their automatic movement.

By comparison, quartz watches tend to be more accurate than mechanical watches because they contain a circuit board and are powered by a battery. While the decision between mechanical and quartz watches remain a personal preference, both movements will provide enough accuracy to keep you on time and ready to take on the day.