well a CB measures two things, heat, and magnetic field (for newer mag-trip breakers) since heat is a product of the number of electrons, as is magnetic field, you COULD say that a CB "counts" electrons, if you were to answer so on a physics test you would get partial credit, as the heat of the bi-metal strip is affected by other factors, such as ambient temperature and heat dissipation, even materials surrounding the CB, or type of metal can have an effect. But of course in chemistry and physics tings on the atomic scale are not observed directly, instead, their effect on other things provides data...
Then of course there's the fact that a circuit breaker has neither the ability to measure, nor record the actual number of electrons.
-Will
