A chemotaxis gradient starts as two checked endpoint signals. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Read two endpoint signals
The left signal is 6 and the right signal is 18 across 6 m.
18−6=12
Difference divided by separation gives gradient
Signal difference 12 over distance 6 m gives gradient 2 per meter.