How many links in the chain?

[pekingduck]

I put the sprockets on when nearly new, less than 500 miles, with the original chain. Remember, the 19T is a little larger, the 37 a little smaller, so they more or less compensate for each other.

The 19T/37T is almost a 1:2 ratio. Manufacturers don't like perfect ratios, since it causes accelerated wear and possible harmonic resonance. A particular chain roller would encounter the same sprocket tooth regularly.