A functional measurement approach to intuitive estimation as exemplified by estimated time savings.

Ratings of time savings when increasing an original assumed mean speed to a higher one were collected for different distances and combinations of velocities. The spontaneous process leading to the formation of an estimate was accounted for by a multiplicative combination of two components, one related to physical distance and the other proportional to the difference in speeds divided by the larger speed. This use of the information of velocities leads to systematic discrepancies between predicted and real-time gains.