Using a Water Level
A water level is a device used for matching elevations of locations that are too far apart. it uses water inside a clear plastic tube with two measuring sticks on either end. Water is the ultimate teller of level and this device is very accurate and can be scaled-up for larger properties by making the tube longer.
(Text Source: A Permaculture Design Course Handbook)
(Picture Source: Bayadaim.org.il)