[pct-l] guidebook elevations

[osprey at att.net (Rick Alway)]

I assume that the mileages in the data book and guidebooks were derived
from a wheel -- is this correct?
 
My primary question: how were the elevations derived? from an altimeter
(which varies as the barometric pressure changes)? or from a topographic
map? I noticed the stated elevations frequently vary from the trail's
placement on topographic maps.
 
Osprey