Because of the economics of cuckoo clock repair, you can easily find old, dirty cuckoo clock movements on eBay for a fraction of what a new movement costs. These movements come with no documentation, so you get to work out which chains, weights, and bellows (cuckoo whistles) are right for them.

In this post I calculate the run time (1 day vs. 8 day) of a cuckoo movement I recently bought, and the Links Per Foot of the chain it uses. These two numbers tell me what parts to buy to make a clock case for this movement.