Measure a coefficient of friction without ever weighing anything. Raise the board slowly until the block slips and read off μs = tan θ; then release the same block and time its 80 cm run with a stopwatch to get μk.
What makes this one different
There are three surfaces — wood, felt, sandpaper — each with its own hidden coefficient. So far, ordinary. The point is elsewhere: a human is holding the stopwatch, and a human hand stops late by roughly the same amount every time.
That fixed delay does not show up as a fixed shift in your answer. At a steep angle the slide is short and a few hundredths of a second are a large fraction of it; at a shallow angle the run is long and the same delay almost vanishes. So your μk rises and falls with the angle and looks like a physical discovery — when it is only the shadow of your own hand.
The Python section hunts exactly that: it searches for the delay which, once removed, makes the answers from different angles agree with one another. This is no longer a plotting exercise; it is what a physicist actually does with spoiled data.