A half marathon is not simply 21 km: its standard distance is exactly 21,097.5 metres. This example keeps the final 97.5 metres in the calculation and shows why a rounded pace display must not replace the exact ratio.
Keep the standard distance exact
Distance is 21.0975 km = 21,097.5 m = 21,097,500,000 µm. Time is 2 hours = 7,200 seconds. The calculation uses those integers before any pace display is rounded.
Read the rounded pace carefully
Exact pace is about 341.2727 seconds per kilometre, displayed as 5:41/km. Per mile it is about 549.938 seconds, displayed as 9:10/mi. Average speed is about 10.55 km/h or 6.56 mph. Multiplying displayed 5:41 by 21.0975 would not return exactly two hours.
Preserve the 21.0975 km finish
Useful cumulative checks include about 28:26 at 5 km, 56:53 at 10 km, 1:25:19 at 15 km, and 1:53:45 at 20 km. The final partial row at 21.0975 km is exactly 2:00:00 after display rounding. The table is an even arithmetic reference, not a pacing prescription.