The pulse sequence accepts only when segment times and echo time close. 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 pulse sequence is a time ledger
The windows are 1 s, 3 s, 1 s, 3 s, and 2 s.
1+3+1+3+2
Total time and echo time are both pinned
The total sequence time is 10 s. The echo time is the symmetric wait 3 s plus 3 s, so it is 6 s.