Built for a runner in the heat

Standard calculators assume a runner holds pace from a 10K to a marathon in cool weather. Viet races in Singapore and Vietnam, where his marathons came out 35–60 minutes slower than those calculators said. This predictor learns from his own races instead.

1. Real course distance. Uses the official distance unless GPS shows the course was clearly short or long.
2. Recent best race. Starts from his best race at another distance in the last 16 weeks.
3. His own fade. How much he slows as races get longer, learned from pairs of his races and blended with results from thousands of Vietnamese marathoners.
4. Heat and sun. Every race is adjusted for the temperature at the nearest airport weather station and the strength of the sun during the race.
5. Current fitness. Adjusted for changes in his Garmin VO₂ Max since that best race.

Every change to the model is tested on all past races before it is used.