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This is a matter of perspective. For example the unit Sievert is an official SI unit despite being just J/kg. This is because confusing equivalent dose and abs
by weinzierl 2y ago
This is a matter of perspective.
For example the unit Sievert is an official SI unit despite being just J/kg. This is because confusing equivalent dose and absorbed dose, which also has the unit of J/kg, could be very dangerous.
Note, that this is different from J sometimes being written as Ws. While there are informal conventions, when we use J and when Ws, using the unconventional one would not be technically wrong because 1 J is simply 1 Ws, whereas 1 Sv is not necessarily 1 J/kg when the later is an absorbed dose.
I think one could reasonably disagree with these decisions but that is how the SI people see it.
- dwattttt 2y ago> This is a matter of perspective. I'd make a stronger statement here; this is a specific example of when having units is most powerful. When even though two things are expressed in some common form, they nevertheless represent something different. > Yeah, but equivalent units with different names is sort of only a display/formatting issue, right? This could be said of two u32s as well.
- pests 2y ago> When even though two things are expressed in some common form, they nevertheless represent something different. This is where people go wrong trying to DRY and other refactors. Slightly forced example but function averagePerClassroom(total) { return total / 30; } // 30 kids per class function averagePerMonth(total) { return total / 30; } // assume 30 "Oh, the function body is the same therefore lets refactor this into an "averagePer" function" expect its two completely different concepts and once the code calculates the actual days per month or once classes are no longer 30 people suddenly things need to be un-refactored, or what I see more often, is just branching off inside the new single function based on an argument flag. Horrible.
- bonzini 2y agoSievert is more of a "newtype" in Rust/Haskell terminology than a separate unit. Likewise for radians and moles.
- loeg 2y agoSure, but I think this is still better than declaring type system bankruptcy because determining whether trees of units are equivalent is hard. You could do newtype wrappers in situations where it is warranted.