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Show HN: I created Units Converter that contains 5000 units across 78 categories

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Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#111

Post by throw_a_grenade »

heisenzombie wrote: post #89
fsh wrote: post #55

Earlier quoted context omitted.

I don't find this rambling insightful at all. Here is what the BIPM actually says about the topic: The SI unit of frequency is hertz, the SI unit of angular velocity and angular frequency is radian per second, and the SI unit of activity is becquerel, implying counts per second. Although it is formally correct to write all three of these units as the reciprocal second, the use of the different names emphasizes the di…

Right, you can explain it but that doesn’t make it elegant. This is the equivalent of a function with a comment in it saying “Here be dragons!”. One very desirable property of a units system is that incompatible quantities have incompatible units. So if I try to add 1 Joule (== 1 kg⋅m^2⋅s^−2) to 1 meter, I’m obviously doing something wrong and I just can’t continue. But in SI I can take 1 Hertz (==1 s^-1) and add it…

This is misunderstanding. There are many situations in SI where two units boil down to the same expression in terms on fundamental units, yet addition does not make physical sense.

More clear example: both Gy and Sv are J/kg (m^2 s^-2), but to add two values, one in each of those units, you need to multiply one of them by a coefficient (that coefficient depends on the kind of radiation and specific organ that absorbed this radiation). So somewhere in the math world lives a constant that is unitless 1, but x Sv/Gy, where x != 1 (again that x depends on circumstances).

Those situations just happen. It's how physics work.

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#112

Post by delta_p_delta_x »

heisenzombie wrote: post #89
fsh wrote: post #55

Earlier quoted context omitted.

I don't find this rambling insightful at all. Here is what the BIPM actually says about the topic: The SI unit of frequency is hertz, the SI unit of angular velocity and angular frequency is radian per second, and the SI unit of activity is becquerel, implying counts per second. Although it is formally correct to write all three of these units as the reciprocal second, the use of the different names emphasizes the di…

Right, you can explain it but that doesn’t make it elegant. This is the equivalent of a function with a comment in it saying “Here be dragons!”. One very desirable property of a units system is that incompatible quantities have incompatible units. So if I try to add 1 Joule (== 1 kg⋅m^2⋅s^−2) to 1 meter, I’m obviously doing something wrong and I just can’t continue. But in SI I can take 1 Hertz (==1 s^-1) and add it…

> incompatible quantities have incompatible units

Okay; how do you add the unit of energy, one joule, to the unit of torque, one newton-metre?

Both have the same SI units: kilogram square metre per second per second. But one is a scalar quantity, whereas the other is a vector quantity.

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#113

Post by BenjiWiebe »

bashinator wrote: post #64
KodyBerns99 wrote: post #42

Earlier quoted context omitted.

May be number of units and categories it supports. Plus I am adding more units.

I couldn't find a way of converting from US teaspoons to cubic light-seconds, which is my favorite demo of the GNU utility. Also, do you have a way of adding a time dimension to the conversions? E.g from kibibytes per day to megabits per second?

My favorite is millilightsecondsmiles, for calculating maximum distance to a server or minimum possible latency for a distance.

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#114

Post by BenjiWiebe »

tzs wrote: post #61

It looks quite extensive, and should cover almost all practical cases. The main limitation I see is that it seems you are limited to picking the units to convert between from predefined lists. If someone gave you say a volume specified in nmi ft^2 for instance and you wanted to convert it m^3 you'd have to do nmi to m and ft^2 to m^2 and then multiply the results to get nmi ft^2 to m^3 because nmi ft^2 is not on the…

I suppose you are aware of this, but GNU units perfectly handles both of your examples.

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#115

Post by jonwiseman »

whatshisface wrote: post #100
jonwiseman wrote: post #93

Earlier quoted context omitted.

That sum to me is both physical and not nonsense, and I think your interpretation is wrong. 1 radian/second != 1 s^-1, but instead ≈ 0.159155 Hz. This is from interpreting a radian as a ratio, in which "doing" one radian in one second is only going over 1/2pi of a whole in a second. So 1 Hz + 1 radian/second, physically and sensibly to me, means ≈ 1.159155 Hz.

I am afraid you may have misunderstood them. It's not that you can't add a centimeter to an inch, it's that you have to convert units first. The unit symbols are intended to help indicate when a unit conversion would be necessary. What many find confusing is the fact that Hz and rad/s are both (in terms of basic physical units) advertised as s^-1. To resolve the issue, you could define 1Hz as 2pi/s on the grounds tha…

I might have misunderstood them, but I tried to argue that I was indeed converting units. Namely, 1 inch + 1 cm = 1.254 in (cm->in implicitly converted).

Also, defining a Hz as 2pi/s seems to be mixing units and quantities, like a Hz is 2 [pi/s] (where [] stores units), where pi is a unit equal to 6.28 [unitless]. Intead, defining a Hz as 2pi/s is to me changing the definition of Hz, unless it's like 2pi / 2pi [1 / s]. >You could also define one rad/s as 1/(2pi s) I was, specifically 1/2pi [1/s].

But as to your point that things like Hz are semi-meaningless unless attached to physical concepts, I'll agree with that (using a potentially different definition of semi-meaninglessness.)

My original statement that 1 Hz + 1 radian/second (i.e. 1 [1/s] + 1/2pi [1/s]) is both physical (semi-meaningless, meaning somewhat meaningful and fully meaningful when we flexibly attach it to a large range of physical concepts) and non nonsense (again, semi-meaningless until we attach to a physical concept) I think still hold.

The key to me is that we can attach physical concepts to units and measures flexibly (but not arbitarily). Hz is indeed applicable to non-sin functions, like square waves, but then we're all of the sudden talking about "the Hz of the nth harmonic of the square wave" (which has loads of relationship to angles).

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#116

Post by somat »

wombatpm wrote: post #67

As a chemical engineer, we would joke about using the worst units in problems. Had a professor specify a volumetric rate in hogsheads per fortnight for a problem once and density in stone per cubic rods

I just saw a fun video on the subject. So if you have not seen it here it is.

https://www.youtube.com/watch?v=kkfIXUjkYqE

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#118

Post by nebula8804 »

Two notes: When I search for oz and ml nothing comes up. Also there should be a button to swap units like you have on xe.com (ability to swap currencies).

Many cooking utensils I have at home are either in ml or oz but not both.

Re: Show HN: I created Units Converter that contains 5000 units across 78 categories

#119

Post by beojan »

SAI_Peregrinus wrote: post #104
saalweachter wrote: post #85

Earlier quoted context omitted.

Teaspoons aren't particularly common in the US. If you do need to stir a beverage or add sugar, you typically use a tablespoon.

Tableware sets in the US commonly come with at least two different sizes of spoon. These usually bear no relation to the "measuring spoons" used to measure volume, though they are handy for stirring tea or eating soup (for the small & large spoons, respectively). For people who cook in the US, a set of "measuring spoons" is a very common kitchen tool. "Teaspoon" and "Tablespoon" are units of measurement of volume, no…

The one you stir tea with is also probably smaller than a teaspoon (probably about half a teaspoon).
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