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Interesting idea. We generally just say "unit" if necessary.

>In 2004, a report to the International Committee for Weights and Measures (CIPM) stated that response to the proposal of the uno "had been almost entirely negative", and the principal proponent "recommended dropping the idea".[15] To date, the uno has not been adopted by any standards organization, and it appears unlikely that it will ever become an officially sanctioned way to express low-value (high-ratio) dimensionless quantities. The proposal was instructive, however, as to the perceived shortcomings of the current options for denoting dimensionless quantities.

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Quite. Unit is quite literally the same as Uno if you squint a bit. Both are Latin derived and both mean "one" - more or less. However I will accept that unit is overloaded somewhat and I don't know much about the way that Spaniards use uno in their spare time.

So using a word that means one and then fiddling around with prefixes is either really clever or really daft depending on which side of the bottle of wine you happen to be.

On balance, for me, I'd be grateful if you leave one alone. To me it means a Platonic One which is unobtainium but I'll let you have one anyway! But only the one (no not that one, the other one.)

I'm Italian, where uno also means uno, so I'll offer my perspective.

As a kid I was taught to use "unità" (unit) to refer to the numbers below ten (e.g. "add up the units first, then carry the tens..").

It is also used as an "accounting" unit (e.g. "there are 3 units left") in some cases, tho probably less commonly than in English, as it's often implicit.

So yeah, unit seems a clear better choice than abusing the number one.

> As a kid I was taught to use "unità" (unit) to refer to the numbers below ten (e.g. "add up the units first, then carry the tens..").

Arithmetic instruction in English uses "unit" in the same way. However, since "unit" is a highly overloaded term, I think the idea of "uno" is a good one, at least for English. For Italian and Spanish, etc., probably not so much.

The biggest conflict I see is in many fields were you are dealing with dimensionless numbers, you are dealing with a lot of them once.

Having to specify "With a Reynolds number of 1300 U and a Prandtl number of 1 mU" is a lot more cumbersome than common convention of "With Re=1300 and Pr=1e-3".

There's also the problem that 1U×3U=3U² and the fact that you wouldn't be able to add 3U² to 2U since the'd be different units.

This isn't a problem in practice though, you just get "strange" constants with units equal to some negative power of U in your equations. The same thing happens when you move from electrostatic units to SI: suddenly Coulomb's constant appears. Many people advocate ESU for precisely that reason: no Coulomb's constant.

Aye, but 1^2 is 1,so it's a bit of a special wash. Like 0!.

The problem is that U isn't 1, it's meant to be a unit, but then it doesn't behave like a unit in which case, why bother with it at all?

That's not how you'd use it. It's a "dimension" for dimensionless numbers. You don't append measures of length with "length" or volume with "volume" but with the actual units of length or volume.

I developed code to do unit conversions and I do include a "dimension type" for dimensionless numbers, which is effectively a 1.

how is 1 mU more cumbersome than 1e-3? The whole point of the prefixes is to avoid those cumbersome exponents, isn't it?

In structural engineering, strain is a unitless quantity (length expansion per unit length) and in my aerospace job we would express parts per million of strain as microstrain.

(I expressed my pitiful raise as 20000 microstrain.)

Sometimes we keep the units though, and express strain in mm/mm. "The strain limit for S355 is about 0.02 mm/mm." A mathematician might eliminate them against each other, for a phycisist it's a reminder of what its definition.

Good point. I also really shouldn’t say strain is unitless, just a case where the units happen to divide out.

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