[crimony]

I'm regularly reminded of the "Alan's editorializing" commentary in the "units.txt" file, which contains gems such as:

[in candela := cd]: "I think the candela is a scam, and I am completely opposed to it. Some good-for-nothing lighting "engineers" or psychologists probably got this perceptually-rigged abomination into the whole otherwise scientific endeavor...

...What an unbelievably useless and stupid unit."

[and in Hertz := Hz]: "Here is YET ANOTHER place where the SI made a really stupid definition...

... Either way, if I ever develop a time machine, I'm going to go back and knock both groups' heads together. At a frequency of about 1 Hz. Or better yet, strap them to a wheel and tell them I'm going to spin one group at a frequency of 1 Hz, and the other at 1 radian/s and let them try to figure out which one of those stupid inconsistent definitions means what. Hint: It'll depend on which time period I do it in, I guess, thanks to their useless inconsistent definition changes."

[lioeters]

Not sure I understand the second quibble. 2π radians per second = 1 hertz seem simple enough?

[jml7c5]

I believe his complaint is that SI defined 1 Hz as 1/s, not as 2π/s. So 2π Hz in the new definition is 1 Hz in the older.

It does make the Hz unit a bit redundant (saying "hertz" is no faster than "per second", and tends to obscure rather than elucidate). Though I do believe it ultimately has saved confusion as it means the 2π multiplier must be explicit,, which prevents accidental confusion between cycles per second and rate of rotation.

[lioeters]

Thank you, after reading the above, I went to the source, Alan Eliasen's units.txt.

You're right, there's a history of changing standards. Without having much familiarity with the topic, I'm inclined to agree that the unit of frequency based on cycles per second, in radians, is more consistent than a "radian as the dimensionless number 1" per second.

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https://gist.github.com/cyrex562/6c7a7cdae68583c02f42658b32e...

The Hz is currently defined simply as inverse seconds. (1/s). See: http://physics.nist.gov/cuu/Units/units.html

The base unit of frequency in the SI used to be "cycles per second". This was fine and good. However, in 1960, the BIPM made the change to make the fundamental unit of frequency to be "Hz" which they defined as inverse seconds (without qualification.)

Then, in 1974, they changed the radian from its own base unit in the SI to be a dimensionless number, which it indeed is (it's a length divided by a length.) That change was correct and good in itself.

However, the definition of the Hz was not corrected at the same time that the radian was changed. Thus, we have the conflicting SI definition of the radian as the dimensionless number 1 (without qualification) and Hz as 1/s. (Without qualification.)

This means that, if you follow the rules of the SI, 1 Hz = 1/s = 1 radian/s which is simply inconsistent and violates basic ideas of sinusoidal motion, and is simply a stupid definition. The entire rest of the world, up until that point, knew that 1 Hz needs to be equal to 2 pi radians/s or be changed to mean cycles/second for these to be reconcilable. If you use "Hz" to mean cycles/second, say, in sinusoidal motion, as the world has done for a century, know that the SI made all your calculations wrong. A couple of times, in different ways.

This gives the wonderful situation that the SI's Hz-vs-radian/s definitions have meant completely different things in the timeperiods:

* pre-1960

* 1960 to 1974

* post-1974