Hacker News Reader

Comment by canucker2016 | Hacker News Reader

canucker2016

For fast connection in time of emergency, calling 999 (or worse 000) on a rotary-dial phone seems tortuous - '9' - followed by several agonizing moments as the dial returns to its resting position, only to have to repeat it two more times?

Touch-tone dialing makes all the emergency numbers O(1) instead of O(N).

View on HN

The standard pulse rate is 10 pulses per second. So 999 takes a bit more than 3 seconds to dial. Three seconds is no doubt a long time subjectively in an emergency -- but it is still much shorter than what it replaced -- calling the full number for the the police/fire/hospital, or asking an operator to connect you.

Also in the olden days, call setup and tear-down could take quite a while. Digits to forward and relays to toggle. It could be easily half a minute before the other party started to ring, especially at peak times.

I believe the reason that 111 was chosen in New Zealand was because, on the analogue network, '1' was a 'long pulse', where-as '9' was a 'short pulse' (think about how long the dial takes to rotate back to its start position for each number). It was considered more likely that telephone cables swaying in the wind and touching would trigger emergency calls if the emergency number was 999.

Edit: Corrected to 111 for New Zealand, as helpfully pointed out.

000 is used in Australia 111 is used in New Zealand

Brits went with 999 because it was easy to convert payphones from allowing 0s to be dialed for free (allowing users to call the operator) to allowing 0s and 9s to be dialed for free. In the UK, the system was that X pulses would be sent to send the digit X (10 for 0). NZ was using British exchange equipment that would recognize three sets of nine pulses as the emergency number, but NZ dial phones used the reverse convention (10-X pulses) so that mapped to 111.

It was a feature not a bug. 999 is the least likely to be made in error, and you even had time to stop the dial in the middle of that last 9.

Reply on news.ycombinator.com