On Sat, Jan 26, 2013 at 4:29 PM, Eric Walker <eric.wal...@gmail.com> wrote:

> Interesting discussion.  It raises for me, among other things, questions
> about the limits of the instruments used to determine the mass of the
> various particles being discussed.

I think this is used for the proton:

http://en.wikipedia.org/wiki/Penning_trap

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