Coverage is a checked read-base ratio shown alongside physical map capacity. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Eighteen reads make a nine-fifths coverage row
18 reads at 100 bases per read make 1800 bases against a 1000 base genome, or 9/5 times coverage.
18⋅100/1000=59
Twenty reads make exactly two-times coverage
20 reads make 2000 bases, so coverage is exactly 2 times. The chip grid carries 16 addresses.
20⋅100/1000=2
Thirty reads make three-times coverage with a larger grid
30 reads make 3000 bases, coverage 3 times, and the 5 by 4 chip gives 20 addresses.