A macrostate probability begins as a finite 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
A macrostate is a counted bucket
The checked ledger groups four microstates into heads-count buckets.
Ω=4,P(H=1)=42=21
The probability is not a caption
The diagram's probability label is derived from the same count ledger.