Annihilation passes the first audit because the electron charge -3 and positron charge 3 add to a visible zero ledger. These scaled charges are exact model labels for the lesson, while real reaction evidence comes from measured tracks, energies, and detector resolution.
Scaled charge makes an electron-positron reaction an exact ledger. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Opposite charges add to zero
The electron has scaled charge -3 and the positron has scaled charge 3, so the input total is 0.
−3+3=0
Two photons carry zero scaled charge
Each photon has scaled charge 0, so the output total is also 0.