Tunneling starts here as an exact finite model, not a material calculation. 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 barrier can leave a nonzero tail
This toy model gives a transmitted probability of 1/4. That is not a real material constant; it is the declared exact model.
T=41
The tail row is small but nonzero
The toy split shows reflected, transmitted, and total rows before any material claim is made.