Using the Checkpoints on Race Day
The 10K, Half and 20 Miles elapsed times work the same way a pace band does: at each course marker, glance at the race clock and compare it to your target. The marker is your reference point, not the watch's lap alerts.
Why Marathon Pace Slips After a Fast Start
Santos-Lozano et al. (2014) in the International Journal of Sports Medicine analyzed 190,228 New York City Marathon finishes from 2006 to 2011 and found that runners at every level slowed as the race progressed, with faster finishers varying least between segments.
Barry Smyth's 2018 analysis of 1.7 million recreational marathoners, published in the Journal of Sports Analytics, found that starting too quickly can result in poorer finish times. Even pacing is the floor; the individual goal-time pages address how to structure a slightly faster second half.
How Warm Weather Changes Marathon Pace
Ely et al. (2007) tracked seven marathons and found a progressive slowing of performance as the WBGT, a heat-stress index combining temperature, humidity, sun and wind, rises from 41°F to 77°F, with finishers from 25th to 300th place slowing more than faster runners.
El Helou et al. (2012) examined 1,791,972 finishing performances across six major marathons from 2001 to 2010 and found that speeds fell and withdrawals rose above each performance level's optimum air temperature, which sat at about 43°F to 45°F for every level except the top 1%.