Another useful trick: plot the same data several ways (e.g. if you were playing with Moore's law you might plot (log) {transistors/cm²,"ops/sec","clock speed","ops/sec/$" etc.} their inverses vs time, as well as things like "how many digits of π can you compute for $1", "multiples of total world compute in 1970") and do the same extrapolation trick on each.

You _should_ expect to see roughly comparable results, but often you don't and when you don't it can reveal hidden assumptions/flawed thinking.