Updated: Aug 1
Mechanical Clocks (and Watches) are an amazing engineering achievement.
(There's a bonus link at the end of this post, explaining this wonder.)
The way the wheels fit together, and work smoothly together to make the clock accurately show the current time, and the progress of time - is just short of miraculous.
Every wheel has the exact number of teeth (called cogs) it needs - being short one tooth is bad, and having an extra tooth is just as bad...
Its placement is super-accurate - move it even a millimeter - and the clock simply won't work.
The wheel's size is critical - being a different size will wreak havoc (cause a "balagan") in the mechanism.