Three coverage rows make the reject, equality, and pass boundary visible. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Sixteen unique reads are below the minimum
The rejected row has 16 unique reads. With read length 50 and genome size 400, coverage is 2x.
16⋅50/400=2<3
Twenty-four unique reads meet the boundary
The boundary row has 24 unique reads and exactly 3x coverage, so equality accepts.
24⋅50/400=3≥3
Thirty-two unique reads clear the same gate
The high row has 32 unique reads, giving 4x coverage and accepted bit 1.