6 ms·
The "two wrongs" hostname is apt. Hertz is for periodic phenomena; becquerel is for radioactive decay. The SI brochure discourages the use of counting units s
by DaveFlater 3y ago
The "two wrongs" hostname is apt. Hertz is for periodic phenomena; becquerel is for radioactive decay. The SI brochure discourages the use of counting units such as 'request'. The number of requests is regarded as just a number, or at best a quantity that is referred to the unit one. The applicable SI unit therefore is just the reciprocal second, s^(-1).
In practice, counting units are used everywhere (e.g., in MB/s, the byte is a counting unit), but I am relaying what the SI brochure actually says on this question.
Ref: https://www.bipm.org/en/publications/si-brochure/ https://www.bipm.org/en/publications/si-brochure/
- basil-rash 3y agoNo way the same org that named the mole a unit discourages the use of counting units. I think what we are really after is yoctomole Becquerels.
- krastanov 3y agoInterestingly, a "conservation of matter" law can exist independently of atoms. I.e. it is mathematically consistent to create a universe in which a "mole" is necessary, but matter is not discrete. Therefore "mole" can be considered a bit more fundamental (in any universe). I find it reasonable to stick to using a "mole" unit on that basis, although I would not be dying on this hill.
- roland_nilsson 3y agoThe yoctomole is a wonderful unit, for example when you want just slightly more than half a cup of coffee! But the mole as a "counting unit" is different from OP's idea of assigning units to things like network requests. The mole is just a shorthand for a number, like a dozen or a score. We don't have different kind of "moles" for, say, carbon atoms and water molecules. Or coffee.
- jameshart 3y agoIt can, in my experience, be very useful to introduce a unit for ‘requests’, as well as one for ‘CPUs’. It lets us produce dimensionally valid formulae for relating request rates (in requests per second) to compute requirements (in CPU seconds per request), data transfer (in bytes per request), and bandwidth (in bytes per second). I kind of wish software engineering’s computer science underpinnings offered a few more of the kind of notational underpinnings that physics offers mechanical or electronic engineers. Why don’t we have a standard set of letters for representing data sizes, requests, compute units, etc; and a set of widely known formulae as familiar to every programmer as V=IR is to an electrical engineer? The only standard symbol computer science has given us (or maybe more accurately that we have taken up) is n, as in O(n), for collection sizes. I wonder if we can do better?
- DaveFlater 3y agoISO 80000 Part 13 gives some symbols within the scope of communication technology (its scope is more narrow than its title would suggest). The standard itself is copyrighted but the quantity symbols are listed on Wikipedia, https://en.wikipedia.org/wiki/ISO/IEC_80000#Part_13:_Information_science_and_technology https://en.wikipedia.org/wiki/ISO/IEC_80000#Part_13:_Informa... See also https://www.nist.gov/publications/quantities-and-units-software-product-measurements https://www.nist.gov/publications/quantities-and-units-softw...
- jameshart 3y agoThat is fascinating. Are there any examples of ‘fundamental laws’ expressed in these terms?
- DaveFlater 3y agoBeing careful to distinguish 'fundamental laws' from just 'quantities that we defined', information theory and queueing theory have some good examples of proven laws.
- boolemancer 3y agoPersonally I like variable names better than symbols anyway.
- asveikau 3y agoA cpu second means very little without more context. CPU performance depends a lot on things like cache, branch prediction, out of order execution. Each second represents something fairly distinct from the others.
- jameshart 3y agoIt’s not ambiguous when the Amazon bill arrives.
- nyrikki 3y ago
- Kwpolska 3y ago[flagged]
- thaumasiotes 3y ago> Hertz is for periodic phenomena > The applicable SI unit therefore is just the reciprocal second, s^(-1). That's the hertz.
- petschge 3y agoWhile Hertz are 1/s, there is implications between using frequencies in Hertz and rates in 1/s. Units are not just something to mechanically check, but also for communication with other humans. So connotations matter in addition to denotation.
- DaveFlater 3y agoHertz, becquerel, et al. are algebraically defined as s^(-1) yet intended to be used for different kinds of quantities. The SI brochure also allows replacing radian by 1, which brings angular velocity into the fight. Further reading: https://doi.org/10.1088/0026-1394/52/1/40 https://doi.org/10.1088/0026-1394/52/1/40
- jameshart 3y agoAnd that brings up the difference between frequency and angular frequency. When you use hertz meaning ‘cycles per second’ it’s far more natural to associate it with an angular velocity of 2pi radians per second - which throws a bit of a spanner in the dimensionless works, and makes it feel like using 1/2pi as a radian makes more sense. Score another point for tau I guess.
- OskarS 3y agoWould you say that one watt is equal to one joule-hertz?
- wnoise 3y agoIn exactly the same way that a torque measured in newton-meters can as easily be measured in joules.
- Terr_ 3y ago
- charles_f 3y agoHertz is the SI unit of frequency.
- msylvest 3y agoWithin the area of viscosities reciprocal seconds is an accepted standard unit