A delay-budget scan compares the same path delays with tighter clock periods to see when setup slack moves from pass to boundary to fail. The slack arithmetic is exact only for the declared stage delays, setup requirement, ideal clock period, and deterministic edge timing; real timing closure adds jitter, skew, load-dependent delay, threshold variation, PVT drift, clock distribution error, and time/voltage measurement uncertainty.
The same delay chain passes, touches the boundary, then fails as period tightens. 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 ten-second period leaves two seconds of delay margin
The stage delays stay 1, 2, and 3 seconds. Period 10 seconds gives budget 8 seconds and slack 2 s.
10+(−2)=8s,8+(−6)=2s
An eight-second period uses the whole delay budget
The stage delays stay 1, 2, and 3 seconds. Period 8 seconds gives budget 6 seconds and slack 0 s.
8+(−2)=6s,6+(−6)=0s
A seven-second period makes the same path fail
The stage delays stay 1, 2, and 3 seconds. Period 7 seconds gives budget 5 seconds and slack -1 s.