The balance wheel is the "heart" of the watch. It beats a certain number of times per second, like a pendulum, keeping time.
Most modern watches beat between 18,000 and 28,000 times per hour—the faster the beat, the more accurate the watch, though also the more delicate. Our 6497 is a slow-beat watch, so it's of the 18,000 bph variety.
The balance is the most delicate part of the watch, and we're lucky to be starting on it so quickly. So far we're assembling (with a staking set, more on that later) and trueing them (making sure they spin perfectly flat). While the most important part of a balance is how well it keeps time, that will come later.
To true a balance wheel, you do something unusual for watchmaking: you use your hands. The balance is seen here in a trueing caliper, which has jeweled pivots and a flatness gauge. As the wheel spins, the rim will raise or lower from the pointer, allowing you to judge trueness. If there's no change, it's true. If the air gap changes, you have to fix it.
When you find the lowest point on the wheel, simply take your finger and (gently) bend the wheel downwards slightly. This will correct the wheel's position on the staff, straightening it out.
It's a bit crude, but it works. We'll be doing even more adjustments soon.
Watchmaking student at the Lititz Watch Technicum, formerly a radio and TV newswriter in Chicago.