Coverage becomes a clearer instrument ratio when read count and read length are scanned separately. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Coverage is a ratio of read bases to genome bases
The genome length is held fixed at 1000 bases. Read count and read length set the numerator.
c=GNreadsLread
Three read plans make three coverage rows
The scan separates more reads from longer reads. Either one can raise the read-base numerator, but the coverage formula is the same in every row.
Nreads102020Lread100100150c123
Longer reads can raise coverage without more reads
The third row keeps the read count at 20 but raises read length to 150 bases. Coverage becomes 3 times.