It was a dark and stormy night when Clark W. Griswold, Jr.
> wrote:
>> I seem to recall that the old Bell System spec for tone duration was
>> 20ms, or 1/5th of a second.
> That would be 1/50 of a second. Maybe it was 200ms?
Switch spec called for 35ms.
Original Hayes Smartmodems defaulted to 70ms of tone, with 70ms space between digits.
Some C.O. equip would detect reliably on bursts as short at 25 ms. I never ran into a switch that would accept dialing at 20ms.