This table, from the Bell System 1969-1970 Switched Telecommunications Network Connection Survey, indicates the time which elapsed between dialing the last digit of the telephone number and the receipt of a test tone supplied by automatic answering equipment at that number
. This time includes a 100 msec delay for the equipment to apply the tone. The standard deviation is affected by the ringing cycle - typically 6 seconds with 2 on, 4 silent.
| Conn Length (airline miles) | Mean (seconds) | Std Dev (seconds) |
|---|---|---|
| All | 11.7 ± 1.8 | 4.3 |
| 0-180 | 10.7 ± 1.5 | 3.7 |
| 180-725 | 14.7 ± 3.2 | 5.0 |
| 725-2900 | 13.9 ± 2.6 | 4.5 |
Copyright 1999-2009 Mark Wahl. All rights reserved.