A directional bias becomes displacement only through a counted run 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
Count forward and backward runs
There are 5 forward runs and 3 backward runs.
5+(−3)=2
Excess runs times run length gives net displacement
Two excess forward runs of 12 m give net displacement 24 m.