Iterum builds new watches from vintage mechanical watch movements. This page contains definitions of terms that might be used when describing the movement of an Iterum watch.
Automatic watch - A mechanical watch in which the mainspring is wound using a mechanism powered by the movement of the user's arm. Usually this mechanism is an oscillating weight that rotates around the center of the movement. As the wearer's arm moves normally throughout the day the weight swings from side to side. Gears connected to the weight wind the mainspring. A slipping clutch prevents the weight from adding more torque to a fully wound mainspring. The alternative to an automatic movement is a manual wind movement where the user winds the mainspring by turning the crown of the watch.
Balance and Balance spring - The balance spring is attached to the balance wheel which oscillates back and forth in a running watch. Each oscillation allows the gear train of the watch to advance a set amount moving the hands forward.
An old film from Hamilton uses a large scale watch movement to show the function of the balance along with the rest of the gear train.
Barrel - The mainspring barrel houses the mainspring. Winding the watch turns an arbor which winds the mainspring. As the mainspring unwinds, the barrel rotates and drives the movement.
Hacking seconds - A watch has a hacking seconds movement if the second hand is stopped when the crown is pulled out. This is normally achieved by pressing a lever against the balance wheel stopping it from turning. When the crown is pushed in the balance wheel is allowed to rotate and the seconds hand begins to move again.
Jewel - Usually made out of synthetic saphire, a jewel provides a hard, smooth surface reducing friction on moving parts of a watch. Most jewels in a watch provide holes for the piviots of wheels to rotate within. Low-cost movements might simply have holes in the metal plates which produce more friction and wear our much faster than jewels. wikipedia
From Elginwatches.org - Why watches have jewels
An Elgin film from the 1940's(?) that takes the viewer from the entire process of how they make jewels for their watches.
Mainspring - The mainspring is the power source for a mechanical watch. Winding a watch coils the mainspring building up potential energy. The controlled release of this energy drives the timekeeping function of the watch.
Shock protection - The pivots of a balance wheel staff are quite thin to minimize friction. Unfortunately, this makes the pivots delicate and susceptible to breaking when the watch receives a shock. Small springs are used on the balance jewels to provide some shock absorption and help prevent broken pivots.
Sweep seconds (center seconds) - A sweep seconds hand rotates around the center of the watch like the hour and minute hands. The seconds hand used to be found at the 6 o'clock or 9 o'clock positions (called a sub-seconds movement) due to the layout of the wheels in a watch movement. Applications that required more precise measurement such as a doctor measuring the pule rate or a soldier counting the time between seeing an explosion and the sound it produced, encouraged the seconds hand to move to the center of the dial. Having the seconds hand sweeping across the entire dial gave the owner a much more accurate view of the passing seconds.