A nucleus identity begins as an exact count 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
Mass number splits into proton and neutron counts
A training nucleus with mass number 14 and proton number 6 has neutron count 8.
14=6+8
The element label is the proton count
The proton count 6 identifies the element in this training ledger.