4 ms·

I think there are some important steps between Maxwell and 1950 that are worthy of mention. Black's paper on negative feedback amplifiers, for one; the inventio

• Animats 7y ago
  Maxwell had P and I, but not D. Derivatives are hard to do mechanically, tend to be noisy, need filtering, and thus have lag. An aircraft vertical speed indicator is one of the few widely used mechanical differentiators. Enough gain to allow throwing it away with negative feedback to get linearity was a ways off in 1868.