telephone dials

There actually is a VERY good reason why the 0 is last on a rotary dial phone. In pulse dial telephones, the number 0 consists of 10 pulses. It could not come first with forcing the redesign of the pulse dialing system, as zero pulses means you havent dialed anything, not that you’ve dialed 0. If 0 were first, 1 would now be 2 pulses and so forth.

note you can manually dial the operator by clicking the switchhook of a telephone 10 times.


That’s an interesting observation, Michael. And in all likelyhood the correct reason zero is placed after nine on the dial - a simple mechanical requirement. Thanks for your contribution.

And here’s a link to the pertinent staff report.

I’ll confirm it. Early “step by step” switches, in fact, were intended to be operated by subscribers rattling the switch hook. The mechanical dial was introduced as a way of automating the process, and making the pulses received more consistent. Among other things, this allowed later switching equiptment to operate off quicker pulses.

There’s still a fair amount of tolerance in the pulse width, evidenced by the fact that you can still “dial” by rattling the hook, and by the habits of a couple people I’ve known who, unhappy with the amount of time it would take the dial to return, would dial with a pencil end and physically drag the dial back to its return position faster than it was meant to go.

More interesting, is, “Why dial ten pulses for ‘0’ instead of just ‘N+1’ for each digit?”

Consider the telco’s motivation for direct-dialing: sure, it saves the customers time, and makes them happy; but more importantly, a collection of springs, solenoids and contact bars or leaves, with no kids to feed, is cheaper to maintain than a human operator!

This implies that one should make it as difficult as possible to accidentally dial the operator, by banging on the switchhook, without eliminating the capability to make an emergency call from a phone with a broken dialing mechanism–hence, ten or more pulses.

As for the DTMF (Dual-Tone, Multi-Frequency, aka “TouchTone[TM]”) keypad arrangement: one source of the “dialing errors” mentioned in the staff report, was that the CO would miss digits keyed too quickly (solenoids and springs are only so fast).

Secretaries and cashiers, whose productivity (and therefore, livelihood) had already come to depend on being fast on a ten-key pad, long before DTMF dialing was rolled out, would actually “outrun” the switch!

There’s probably someone at Bellcore, that has all the details neatly filed away, somewhere; but whoever first dealt with all this has probably long since retired or deceased.

Subscriber m23 is right on track… The dailing system used a “complement-of 10” sysyem…

.i.e. 7 dailed gave 3 pulses.
6 dailed gave 4 pulses
3 dailed gave 7 pulses

This was to accomodate a mechanical device at the local telephone exchanges, known as a ‘Uniselector’

A Uniselector could be likened to a car’s engine distributor, if the engine had about 150 cyclinders!

I’m pretty sure this is wrong.

Dialing a 7 gave you 7 pulses, a 3 gave you 3 pulses, and so on. The reason 0 gave you 10 pulses was not because the phone used a compliment-of-10 system, but because 0 was the last number on the dial (where a 10 would have been numerically), whereas all the other numbers were in the order you would expect based on their numeric value.

I took apart telephones as a hobby when I was a kid, and a buddy of mine and I actually built a “linear” dialer. A piece of insulating material about a foot long, with 10 stationary contacts down its length and one moveable contact that slid up and down. You “dialed” by pushing the moveable contact over the appropriate number of stationary contacts. We got so that we could dial complete 7 digit phone numbers with a little practice. This would not have worked if the real phones had used the “compliment-of-10” system A3S talks about.

In short, I’d like to see a cite on that.


I’ve never used a pulse phone per se myself, but my last touch-tone phone had a little switch on the side, and you could set it to emulate a pulse-dialing phone. You could then hit auto-dial and listen to the pulses sound off. They were a little too fast to count, but I definitely remember their being consistent with 1=1, 2=2, 3=3… 0=10, and not consistent with the reverse.

Yep, and the Staff Report is being amended to reflect this info. I didn’t research it when I was writing the report, mea culpa, but I had just tossed in the comment about “0” as an aside without much thought. Shoulda known better.

Thanks for the input.

I remember, when I was in Junior High, thinking I was really smart because I could dial the phone without touching the dial. I did it by depressing the switch-hook the number of times equal to the digit I was dialing, pausing a moment, depressing the switch-hook the number of times to represent the next digit, etc. Boy, was I NEAT to be able to do that!

When I was young (born in 1957) my parents had a lock on our dial phone (it was a cylinder that went into the “1” hole that prevented you from dialing any number greater than 1) because my sisters made too many calls. Like Bindlestiff, I learned that I could still make calls by tapping the switch.

My parents found out, but they didn’t care, because I wasn’t the one making too many calls. Intelligence rewarded–what a concept!

I remember hearing long ago the same reasoning that roesinge gives: people used to numeric keypads were too quick for the early touch tones. I wonder if this actually was a factor or if it is an urban legend.

On the notion that people used to numeric keypads were too quick for the early touch tones:

First, I didn’t run across it in my research, which is not necessarily indicative (absence of evidence is not evidence of absence), but AT&T and related sites didn’t mention this.

Second, and more telling, is that the touch tone phones made their first appearances in the early/mid 1960s, while the electronic numeric keypad (as we know it today) didn’t appear until the late 60s or early 70s, so far as I remember. Thus, the logic here is reversed – the calculator keypads came AFTER the touch-tone phones.

I think this is a re-telling of the bit about about the QWERTY arrangement of typewriter keys, as discussed by Cecil: Was the QWERTY keyboard purposely designed to slow typists?