The forefoot summary measure is the mean of temperatures
taken at five sites on the plantar surface of the foot:
the great toe, the fifth toe, the first metatarsal head, the
fourth metatarsal head, and the fifth metatarsal head. The
plantar summary measure is the mean of these sites and the
plantar heel; the all loci measure is the mean of these sites
and a measurement on the dorsal forefoot.