A midpoint signal is found by multiplying the gradient by the distance from the start and adding it to the start signal, assuming a linear profile. Starting from signal 6 and moving 3 m along gradient 2 per meter gives 2 times 3 = 6 added, for a midpoint signal of 12 exactly for the stated toy interpolation ledger; real fields have nonlinear profiles, noisy signals, receptor adaptation, and calibration uncertainty.
A checked gradient predicts a signal at a measured distance. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Move partway along the gradient
Start from signal 6 and move 3 m along a gradient of 2 per meter.