An entangled pair is represented by one joint amplitude table, not two separately completed single-particle ledgers. The table entries are exact only for the stated basis and amplitudes; real experiments add preparation error, detector inefficiency, basis misalignment, decoherence, and finite statistics.
Two quantum particles can be described by one joint amplitude table. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A pair has one joint amplitude table
The nonzero joint amplitudes sit on the zero-zero and one-one same-outcome cells. Each has probability 1/2.
Psame cells=21
Only the same-outcome cells are populated
The joint table is read cell by cell before any single correlation sentence is made.