`omit-unity-mantissa` for `exponent: "eng"`.

[MiledMFN]

I was looking for a way to apply omit-unity-mantissa for exponent: "eng" or through another approach, even by using a dictionary as num but it seems that isn't possible:

error: module parsing does not contain decompose-signed-float-string
   ┌─ @preview/zero:0.6.0\src\num.typ:96:38
   │
96 │       let (sign, int, frac) = parsing.decompose-signed-float-string(mantissa)
   │                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: error occurred in this function call
    ┌─ @preview/zero:0.6.0\src\num.typ:208:11
    │
208 │     return show-num(it)
    │            ^^^^^^^^^^^^
help: error occurred in this call of function num
    ┌─ @preview/zero:0.6.0\src\units.typ:320:4
    │
320 │     num(value, state: num-state, force-parentheses-around-uncertainty: true)
    │     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Any help, please.

[Mc-Zen]

Hi @MiledMFN ,

you did not give an example of the code that you tried but I assume it must have been something like num[1000]. If you activate engineering notation, this is rendered as $1.000\times10^3$. Note that the digits of your input are kept! In this case, this means that the three zeros from the input 1000 are treated as significant digits of the number. Omitting them with engineering notation would ignore this precision which carries a message in itself.

Now 1.000 is not exactly "unity" although the value is one. It means "1 with a precision of 3 digits after the point".

The way to handle this and still benefit from omit-unity-mantissa is to explicitly reduce the precision to just the single digit and include the shift as an exponent, e.g.

#num(
  exponent: "eng", 
  omit-unity-mantissa: true
)[1e3]

Now, omit-unity-mantissa kicks in as expected.

[MiledMFN]

Hi @Mc-Zen.

Sorry, I've not explained very well. I'm trying to print only the units, for

#let m = zi.declare("m")
#m(
  1e-3,
  exponent: "eng", 
  omit-unity-mantissa: true
)

I want "mm" only but is outputted "1 mm"

[Mc-Zen]

I see. But this means that you only want the unit, without the number? Couldn't you just use zi.mm()?

I admit I do not quit understand the context.

[MiledMFN]

Yes, but I'd like to keep the factor 10^-3 or whatever handled by Zero, and keep the units defined purely without metric prefix.

[Mc-Zen]

Unfortunately, this is not possible. If you tell me your usecase and its context, it might convince me that it is worth to add such a feature but currently this seems too niche to me to add.

Especially since it is very unclear to me how the API should look like.

[MiledMFN]

Here I've written a show rule in which is hidden everything (and including) after the math.dot.op. It's just an extract. But in the table are shown the areas in mm^2, as the column also indicates it. Or also it could be fixed exponent: (fixed: -6).

= Wire Configurations

#set-num(
    omit-unity-mantissa: true,
    product: math.dot.op
  )
#set-round(precision: 3, pad: false)

#let mantissaOnly(mathEq) = {
  show math.dot.op: none
  show math.attach: it => {
      if it.base == [10] { none } else { it }
  }
  mathEq
}

#table(
  columns: (auto, 1fr, auto, auto),
  align: (center, left, right, right),
  table.header([*\#*], [*Wire Configuration*], [*Area $[#m2(exponent: "eng", omit-unity-mantissa: true)[1e-3]]$*], [*Deviation*]),
  ..for (i, (config, area, dev)) in sorted_combos {(
    [#num(i + 1)],
    [#format_conf(config)],
    [#mantissaOnly(num(area, exponent: "eng"))],
    [#num(dev)]
  )}
)

[Mc-Zen]

I see. But your prefix is effectively fixed - you decided that this column is to be given in square millimeters and no automatic detection is performed. Do I understand correctly?

In your case, I would just define this precise unit "mm^2", including the prefix. For the data, I would multiply the values by a corresponding factor of 10^3 and pass these preprocessed values to num. After all, you don't really want the automatic engineering exponent for each number individually: all values in the column should be shifted by the same factor. For numbers near a certain threshold this could easily backfire when a few numbers are too large or small and get categorized into a different prefix class.

Your show rules to hide the exponent might break in the future or even if you just decided to switch the product symbol to ×.

This is no criticism by the way, I'm just looking for what exactly might be missing in Zero to achieve this with the most elegant and idiomatic approach!