# Tag Info

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After some significant research, I have figured out how to do this. You make a linear measurement array using precision 1.0000" balls in right angle v-groove with a base plate, and then a matching block at the top. If this is done carefully, you can even reach 1/1000th precision. It looks like this: Everything has to be scraped and square, especially the ...

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is there any requirement to determine (and possibly correct for) the perturbation, or "shift", of any and all primary frequency standards, besides the described "shift due to ambient radiation"? Yes. These are called "systematic errors" and they are the order of business pretty much all day, every day, at the metrology labs that implement frequency ...

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I'm not going to talk about the misunderstanding you have, but about the actual question you asked.The mass energy equivalence equation is $$E^2=(mc^2)^2 + (pc)^2$$ ($p$ is the momentum of the body). If we use specialized units such that $c$ (the speed of light) becomes dimensionless, we can have the same units for mass and energy. (This can be done, for ...

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Is there any rationale from the standpoint of physics to choose candela as a base SI unit? That's still the wrong question. The right question: Why do these standards (any of them) exist? The answer is commerce and industry. The SI doesn't exist to support the sciences; that it does support the sciences is a nice side benefit. It exists to support ...

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Wikipedia gives the origin of the unit, with references, starting from the previous definition of 'candlepower' (based on an actual candle), through the redefinition in terms of a perfect blackbody emitter at the melting temperature of platinum, to the modern definition which may more easily be realised experimentally.

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That definition is for calibration. Luminosity is based on a standardized model of human eye and takes into account sensitivity of human eye to different wavelengths. Two source with the same intensity but different frequency have different luminosity. Luminosity is related to intensity and frequency by the luminosity function.

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It is a fairly good question. Physical quantities don't have dimensions. They have one or more scales, and it is the scales that have dimensions. It is perfectly legitimate to set $\epsilon=\mu=1/c$, which would mean that the unit of charge $Q^2 = \text{Joule-seconds}$. This would derive for the fps system, $1\ \text{verber} = \frac{1}{94.55}\ ... 3 The practice of dividing the degree used to measure angle into sixty minutes of arc, and that into sixty seconds of arc is over 2000 years old. The corresponding practice of dividing the hour used to measure time into sixty minutes, and that into sixty seconds, is over 1000 years old. Why sixty? That's over 5000 years old. The Sumerians and Babylonians used ... 2 It's historical. The second was originally defined so that$60\cdot 60\cdot 24\,\rm s\$ added up to a solar day. But that's a little hairy to measure, because the length of the day varies through the year. The sunrise-to-sunrise time varies from winter to summer. The noon-to-noon time interval, which would be operationally defined as the interval between ...

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