The displayed gap list is bound to transition sources. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The displayed list is not independent data
The upper-to-ground line is listed as 9 joules because its source transition has that gap.
ΔEupper→ground=9J
A stale edited gap is not a renderable state
If that displayed gap were changed without changing its source transition, validation would stop the lesson.