Fails to parse mAh (milliamp hours) about js-quantities HOT 10 CLOSED

This would require adding "Ah" as a unit. We can't simply guess what the combined units mean or we would have issues with things like "mm" (millimeters? or meter*meter?).

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Disambiguating theses cases could be supported by choosing a conventional way to parse them.

For cases represented by joined characters with no separators (other cases are not ambiguous), the first character could be always considered as a prefix (if compatible of course) and the remaining characters would be parsed as raw units. If this convention is followed, we have:

'mm': milli, meter
'm m': meter, meter

'mN: milli, newton
'Nm: newton, meter
'm*N': meter, newton
'm N': meter, newton
'mmN': milli, meter, newton
'mNm': milli, newton, meter

'Ah', // ampere, hour
'hA', // hecto, ampere
'mAh', // milli, ampere, hour

Like so, it seems to follow the principle of least surprise.

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To play devil's advocate here, I would argue that hecto isn't very commonly used and thus hA not being hour*ampere might be more surprising than you would expect (and the same goes for yocto, maybe less so for deci).

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However, when I first started using this library, I was also surprised that this guess-work was not happening. But after looking into it and seeing the ambiguity I decided that wasn't such an issue for me.

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Two arguments in favor of considering "hA" as hecto, ampere:

• Ampere-hour is often, if not always, denoted Ah so considering to parse "hA" as hecto, ampere should not be a real problem for anybody.
• Ruby-units parses "hA" as hecto, ampere and it would be desirable to have the same behavior.

That said, I really appreciate your opinions @rage-shadowman. It is a great help.

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Q: Does ruby-units pars "Ah" as ampere*hour?

If ruby-units does the guess work in this manner, then I agree with you (especially since I see no mention of "Ah" specifically in the ruby-units source). I do not have a running ruby environment to test it out on though.

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No. Ironically it fails to parse it. But it is not surprising because js-quantities regexps were originally the same than Ruby-units ones. However, I would like to fix it because it is a bug.

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Are you sure they consider it a bug in ruby-units? How would you define "hrs" then? hour or hour*second? There are likely many less obvious examples of ambiguity due to all of the aliases that are allowed for each unit. When I looked into making this change I gave up after I found a few that I couldn't state empirically should always go one way.

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I do agree that "Ah" is a commonly used unit and thus may deserve its own unit definition. But I personally think that guess-work which results in direct answers to ambiguous questions is a bad idea.

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I don't really have any authority in this matter, but given the conversation it does seem rage-shadowman's suggestion to give "Ah" its own definition is the solution with the least risk.

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