Treat binding energy as a before-minus-after rest-budget ledger. Four free
nucleons at 5 joules each make 20 joules, and the bound proxy is 17 joules, so
the missing 3 joules is the toy binding budget; real nuclear masses and energies
come from calibrated measurements with unit choices and uncertainty.
Binding energy is taught as an exact before-minus-after 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
Binding energy is the missing rest budget
4 nucleons at 5 joules each make a free budget of 20 joules.
4×5=20
Binding per nucleon stays fractional
The bound proxy is 17 joules, so binding is 3 joules, or three fourths of a joule per nucleon.