A signal-speed-is-not-instant scan fixes a line length and signal speed and checks the one-way travel time t = length / speed, the finite delay before the load sees a launched step. The arithmetic is exact only for the stated lengths, signal speeds, delays, and rows in the ideal uniform-line, constant-speed model. Real lines add dispersion, loss, connector mismatch, finite rise time, cable tolerance, probe/calibration limits, finite precision, and measurement uncertainty.
A long line responds after a finite source-bound delay. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A line delay is length divided by signal speed
A 12 meter line with signal speed 3 meters per second has a checked travel time.
t=12m÷3m/s
The step reaches the load after the checked delay
The one-way delay is 4 seconds, so the load cannot respond instantly.