Programmer productivity measurements don't work.
The most common metric was discredited decades ago, but continues to be used: KLOC. Only slightly better is function points. At least it's tied to some deliverable value. Still, the best function point is the one you don't have to develop. Likewise, the best line of code is the one you don't need to write. In fact, sometimes my most productive days are the ones in which I delete the most code. Why are these metrics so misleading?
Because they are counting inventory as an asset. Lines of code are inventory. Function points are inventory. Any metric that only measures the rate of inventory production is fatally flawed. We need metrics that measure throughput instead.