Each

I believe you've hit it, McTag, when you attribute it to jargon. Probably those who use it in conversation are primarily those who use it at work. If they are use to writing it at work, they probably use it when talking at work, and it just continues away from the workplace.

Flyboy and McTag, I'm curious, have either of you heard the word "niner" used instead of "nine"? I think I have asssociated that word with those who say each in an inventory sense. Also, what does "1 off" mean? I have heard that used and just thought it was an accent for "1 of."

Thanks for helping to unconfuse me on the first issue.

This is a guess, no better than that:

I would say "niner" came to be used on 2-way radio, for extra clarity.
Much in the same way as "Able, Baker, Charlie..." are used to clarify which letter is meant by the caller.

The term "1 off" I have seen on technical drawings, meaning "make 1 off this pattern".

We also use the phrase "He's a one off" meaning, he's one of a kind.

But I agree it's a bit clumsy and also probably a bit unnecessary.

McTag's example is very clear for the usage of each, but the usage in the starting thread has given me a headache. I even don't want to read it twice

"One-off" is usually used to mean an exception, or something that's limited to a single time.

Eg. The death of Peter was a one-off incident.

Just kidding. Here's a clearer example:

The incident with Bill Clinton and Monica Lewinsky was just a one-off thing.

Do you think you are saint or prophet? Monica is Bill's girlfriend. And we cannot be sure if Hillary will sue for a divorce with Bill. But if Hillary will have done... eh, you know what I mean. That thing might be not one-off then.

I agree with McT withe respect to "niner". The term was always used in radio transmission. With limited clarity "nine" could easily be mistaken for "five" (one syllable and internal i) particularly when transmitting a series of numbers as in a call sign or geographical coordinates.

In the same vein, as I recall, telephone operators always say "ni-yun" for "nine", apparently for the same reason.

I thought it might be loosely tied to the german equivalent. "Niner" could bot be mistaken for "No."