Use one ideal moving clock and one lab frame to keep the time ledger visible.
With gamma 5/4, a 4 s interval on the moving clock becomes 5 s in the lab; real
timing comparisons also need synchronized clocks, calibrated paths, finite
resolution, and uncertainty.
A four-second moving-clock interval becomes five seconds in the lab. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.