Holding step length fixed while count changes makes mean-square spread readable. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Two steps make eight square metres
Hold step length at 2 metres. With 2 steps, mean-square spread is 8 square metres.
2⋅22=8
Four steps double the spread ledger
The same step length over 4 steps gives mean-square spread 16. The diffusion coefficient remains 1 square metre per second.
4⋅22=16
Six steps make twenty-four square metres
With 6 steps, the checked spread reaches 24 square metres. This is count times step length squared.