Muon decay is checked with more than one count column: the electron-family and muon-family ledgers each have to close on their own. The small integers make the bookkeeping exact for this reaction model, but real particle identities are inferred from detector signals and carry classification uncertainty.
Muon decay keeps electron-family and muon-family ledgers separate. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Electron-family number cancels
The electron-family output is 1 plus -1 plus 0, giving 0.
1+−1+0=0
Muon-family number remains one
The muon-family input is 1 and the output is 0 plus 0 plus 1.