The problem is the amount of time you spend waiting for the dial to return. At the standard rate of ten pulses per second, you would end up waiting nine pulses

The problem is the amount of time you spend waiting for the dial to return. At the standard rate of ten pulses per second, you would end up waiting nine pulses three times or (0.9 * 3)s plus the pause (approximately 3 pulses wide) for the dial to return, plus however long it took you to finger and wind the dial three times. Could easily take upward of six seconds. 111 (if it could feasibly be allocated) would be the best three-digit code. You would spend the least amount of time rewinding, fingering, and returning. The minimum time per symbol would be 0.1s for the single pulse, ~0.3 seconds for the pause (that section on the dial between the backstop and the 1 digit hole) and about 0.1-0.2s for the finger and wind (reduced due to Fitts's law, and easier for the blind since it is the first hole from the backstop rather than the second). These factors combined could cut the dial time easily in half.