[Electronic M]

Google Hydramatic*. The articles on it are fascinating and informative. The basic system is a hydraulic analog computer that takes output speed, engine speed and often throttle position and calculates what gear is best/when to shift.

* I recently ran a search trying to learn how to start a Hydramatic equipped car (there is a 46 olds with Hydramatic up in Appleton that I've been thinking about getting) and never found an answer to it, but enjoyed the reading enough not to care about my original question. I've read that Nash's with Hydramatic had you push the shifter forward (it normally moves up and down for gear selection) to mechanically engage the starter, and I've read some 40s cars used one of the driving pedals to mechanically engage the starter (the ignition key only controlling whether spark and cabbin accessories operate).