A matched-termination-erases-the-echo ledger shows the special boundary where load impedance equals line impedance, so the reflection coefficient is zero. With both values at 4 ohm, the reflected voltage is exactly 0 V only for the stated ideal lossless-line row. Real terminations include tolerance, connector discontinuities, frequency dependence, line loss, finite rise time, calibration limits, and measurement uncertainty.
A matched boundary sends no voltage step back. 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 matched termination has zero coefficient
When load and line are both 4 ohms, the coefficient is 0.
Γ=0
Zero coefficient erases the echo
The reflected voltage is 0 volts, so this boundary contributes no echo step.