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17

The most precise measurement of the mass of an electron was reported by Sturm et al in Nature 506, 467–470 (27 February 2014), quoting a relative precision of $3\times 10^{-11}$, meaning they determined the mass to better than $3\times 10^{-41}~\rm{kg}$. If that is not the best, at least it gives you an upper bound... Note that if you could weigh such a ...

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Disclaimer: I've never done the particular class of measurements you ask about, but I have done other low raw-rate, precision measurements (neutrino mixing and weak form-factors). The focus of experimental work for low count rates is multi-pronged: Maximize the quantity of data. For counting experiments the raw fractional statistical uncertainty goes by ...

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Many of them are calculated. All the ones that have $u$ or $Da$ as the unit are in atomic mass units, referenced above in the table. They just count up the atoms and add. For bacteria, yeast, and the like it will vary from one specimen to another. Not much precision is quoted and it is likely they use the volume (easy to measure with a photograph) and ...

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It seems to me it might depend on the material the ring made of. After a bit of poking around Amazon book previews I managed to find page 19 of "Physics and Chemistry of Interfaces" by Butt, Hans-Jürgen; Graf, Karlheinz; Kappl, Michael (2003). This is the source cited by the Wikipedia article you got the equation from. The next sentence, immediately ...

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You can think of the force as arising due to the energy associated with the air-fluid interface. The force is a change in energy per unit distance. The surface contact of the fluid with the ring does have an energy associated with it, but this energy is constant as the ring is lifted out of the water, and thus does not contribute to the surface tension. ...

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