Cumulative time is the only honest instrument
Mile-marker pace is polluted by marker placement, GPS drift, and the terrain you just climbed. The watch's cumulative time at each split — programmed from the pace calculator — is ground truth. The plan becomes a lookup table: at mile 9, the watch should read 1:19:30. Simple, checkable, immune to feelings.
Effort checkpoints for the hills
Between split checks, effort (breathing, conversation test) is the instrument: hard uphills at honest effort will read slow and that is correct. Writing "honest 10K effort up the hill, recover on the descent, back on schedule by mile X" turns terrain from a pace accusation into a plan feature.
The three pre-decisions
One: the goal (from an honest equivalency baseline). Two: the split discipline (even or slight negative, written down). Three: the surge rule (when "I feel great" at mile 10 gets permission — a specific checkpoint, not a feeling). Races are won in the decisions made calmly at the kitchen table; the starting line is for executing them.