We all use a watch, whether a wristwatch, a wall-clock or a watch in the mobile phone. However, only few really know how a modern wristwatch measures the passage of time. Watches are very complex machines and most of the documents meant to explain how watch movements and mechanisms work are often difficult to understand and/or to assimilate. On the other hand the mechanic of most common watches is based on very simple principles not that difficult to understand and assimilate. Under this optic, watch movements can be explained in a very simple way and “beginners guide” should start from explaining those overall principles.
We will try to simplify as much as possible the explanation and clarify the way watches measure the passage of time. In a second phase we will go a bit more in details so to familiarize with the most common parts of a watch but we will not cover every single part of a watch movement. Before doing that, let’s clarify that for the purpose of this article we will consider only three types of watch movements: manual and automatic movements and quartz watches. Manual and automatic movements are called mechanical as they are made of only mechanical parts like gears and springs. On the other hand the quartz movements have an electrical circuit but may also have some mechanical parts.
Watch movement principles
To measure the passage of time the watch movement needs to have: i)a source of energy, ii) a mechanism that transforms energy into a regular and continuous signal and iii) a system able to transform the signal into a visual output to indicate the passage of time. Notably, this structure is common to any kind of watch – even the atomic or NIXIE Tube watches are based on the same principles.
The most complicated part resides in the transformation of energy into a regular and continuous signal. The transformation of the signal into a visual output tends to be the same for the three types of movements (manual, automatic and quartz), though some quartz movement might set themselves apart via leveraging liquid crystal display (LCD).
Source of Energy
All watches need a source of energy to operate. Even the most ancient watches like the hourglass or water clocks needed a source of energy to work. The energy needs to be supplied to the watch in a regular and consistent way or the watch needs to be able to accumulate and then slowly release the energy over time.
The source of energy is one of the key differentiating element of the three movements. The most different and simple are the quartz movements in which the energy is supplied by a tiny battery which tend to last 12-36 months.
In the manual movement, instead, the energy is generated by a person who needs to regularly turn the crown of the watch (the crown is a wheel generally located on the side of the watch). Via doing that, the person generates kinetic energy which then needs to be stored and finally released slowly over time. This task is accomplished by a tiny coil-shaped spring called mainspring. As the watch is wound the tension in the mainspring is increased and the spiral get’s tighter and tighter. When the watch runs the tension is released and the mainspring gradually transmits energy to another mechanical system.
Finally the automatic movement is meant to simplify the task of the watch owner and for this reason instead of requiring regular winding of the crown it is provided with a small weighted rotor. The rotor is a half circle-shaped metal weight attached to the movement that can swing freely in 360 degrees. When the person moves the wrist the rotor turns and transmits its movement to the mainspring which winds hence stores the energy.
This means that both mechanical movements use the same system to store and release energy (mainspring) and the only difference is the method used to generate the energy (crown vs rotor).
The manual and automatic movements transform the energy into a regular and continuous signal in the very same way. A train of gears transfers the energy from the mainspring to the escapement wheel which then transforms the rotating motion of the gear train into impulses thanks to a fork element named pallet. In other words, the escapement acts like a brake, taking the energy transmitted from the mainspring and releasing it out slowly over time in discrete impulses.
The escapement is then connected to the weighted balance wheel (and hairspring) which helps regulating the frequency of the impulses. The balance wheel oscillates, in a circular motion between five and ten times per second (half oscillation) and send those regular movements to the mechanism that transforms them into a visual output.
In the quartz watches, the energy is conveyed through an integrated electric circuit to a quartz crystal. Due to its piezoelectric characteristics and as a consequence of the passage of electricity the quartz crystal vibrates at a rate of 32,768 vibrations per second. The vibrations are then transmitted back to the integrated circuit which will convert them back into an electric signal to activate a stepping motor. This motor will move at a regular and constant rhythm and will finally activate the mechanism that generates the visual output.
Notably the mechanical watches are subject to a series of forces that might reduce accuracy or lifetime of the watches. To prevent those forces from limiting the functionality of the movement the watchmakers leverage some more complicated elements. For example the most sophisticated mechanical watches are provided of a tourbillion ('whirlwind' in French). The tourbillon is essentially a cage which houses the escapement and balance wheel. Through its rotation the tourbillion is capable of offsetting the effect gravity hence improves the watch's accuracy. Another element present in mechanical (and sometimes quartz) watches is the jewels. Those are generally synthetic rubies that are set at points of high friction, like the center of a gear that is constantly in motion. These are used to reduce the metal-to-metal friction and wear hence improve performance and accuracy over time.
The mechanism that generates the visual output is the same for the three movements in analog watches. In particular, a series of gears transmit the regulated, equally metered signal from the balance wheel or the stepping motor to the hands of the watch. The gear train will differentiate hours, minute and seconds and ultimately the hands will rotate in the dial to indicate the time.
In the digital watches (based on quartz movement) the signal generated by the integrated circuit goes directly to a liquid crystal display (LCD) without the need of passing through the stepping motor. Some manufacturers develop ana-digi watches in which part of the measures of the passage of time are shown in a LCD display and others in a classic analog display (i.e. rotating hands) – those watches have the signal going both directly to the LCD and to the stepping motor hence to the hands.
Watch movements simplified
The three above described watch movements are more sophisticated than that, and we have simplified in order for you to easily understand the key principles and elements used to measure the passage of time. As you might appreciate by now, the mechanical (manual or automatic) movements are by construction much more complex and require more labor intensive effort – for this reason they are generally far more expensive than quartz. On the other hand the battery-operated watches are more accurate as they depend less from moving parts that are subjects to many external forces.
The above descriptions are based on the simple movements. However, both the quartz and mechanical movements might include complications (any feature beyond the simple display of hours and minutes) and in this case the signal generator and visualization system become much more complicated.
By now you are ready for the “advanced” explanation of the different kind of movements and complications. If interested in understanding more about watch movements keep following us. We might cover more detailed explanations of the different parts of the watch movements in future articles.