The surveyor uses a level
to determine elevations. Levels fall into three broad categories: a
"dumpy" level, a "Wye" (or 'Y') level, and
"automatic" level. As with all tools of the surveyor, there are
various degrees of accuracy within each category of level.
A "dumpy" level
has a telescope with cross hairs permanently mounted in a pair of arms.
A "Wye level has a
telescope with cross hairs that is removable from the arms.
level is basically a dumpy level, but it has a built in compensator that
automatically adjusts for minor errors in the set up of the instrument.
In conjunction with a
level, the surveyor will use a "level rod" to read an elevation up or
down from the level of the telescope. From these observations, a surveyor
can determine differences in elevation of different points or transfer an
elevation from one location to a distant location.