AGL GradeLight 3000, Owner'S Manual

Page: 21 / 40

20
APPLICATIONS
Transfer of Elevation
Using an Automatic Level
1. Mount the level on a tripod outside the
manhole or open cut. Adjust it to level
and point at the manhole hub. Take a
reading from a rod held at the hub. This
reading is sometimes called the “back-
sight” reading. (Figure A)
2. Next take a rod reading at the manhole
center. If a manhole is in place, read
the elevation of the base. In an open
cut it is necessary to place an object in
the cut which can be used as a
reference. A brick, stone, or board
placed at manhole center will work for
marking a reference elevation, and as a
starting point for the placement of the
laser or trivet.
Using the Special Transit and Rod Group
This is an ideal method to use when the offset
hub is too far from the manhole center to
transfer elevation with a batter-board or other
means. The Special transit is set up using the
Rod and Crossbrace System. (Figure B)
1. Mount the Special Transit on the
calibrated rod and point it to the
manhole hub. The top edge of the
transit mounting bracket is the elevation
reference and is the same as the
horizontal crosshair (centerline) of the
transit.
2. Level the transit using the adjust knob
and the level vial. Use the forward
marker knob to adjust the transit to that
it is pointed exactly to an engineer’s rule
or calibrated rod section held at the
manhole hub.
3. After reading the engineer’s rule or
calibrated rod, measure down from the
top edge of the transit mounting bracket
(transit centerline) to the correct invert
elevation.