TB 9-5220-212-40
Use 5-inch base if 8 percent of TI width exceeds 5 inches.
(2) Designate north, south, east, and west as shown in figure 1.
(3) Set up perimeter, diagonal, and centerlines on TI as shown in figure 1, following
sequence listed in (a) through (d) below:
(a) Lay out 2 diagonal lines, making certain that they bisect physical center of TI.
NOTE
Any marks made on TI surface must not be made where base
will travel. If possible, mark only on clamping ledges of TI.
(b) Lay out even number of increments (stations) along each diagonal line,
using length of base selected in (1) above. Each diagonal line will have same number of
stations. Do not extend stations onto clamping ledges of TI.
(c) Lay out 4 perimeter lines connecting with diagonal lines, and observe
conditions listed in 1 through 3 below:
1 Each perimeter line will have even number of stations.
2 No station will extend to clamping ledge of TI.
3 North perimeter line will have same number of stations as south
perimeter line, and east perimeter line will have same number of stations as west
perimeter line.
(d) Lay out centerlines, observing conditions listed in 1 through 3 below:
1 Each centerline will pass through physical center of TI.
2 Ends of centerlines will tie at midpoints of respective perimeter lines.
3 Each centerline will have same number of stations as respective parallel
perimeter lines.
NOTE
Make certain that end stations of perimeter lines tie in with
end stations of diagonals and that end stations of centerlines
tie in with midpoints of perimeter lines as closely as possible.
(4) Place differential electronic level heads A and B at center of TI adjacent to
northwest to southeast line. Adjust zero control for 0 (midrange) indication on each head.
Set polarity switch head B to REV and HEAD SELECT switch to BOTH.
NOTE
Both heads must be parallel to line of movement and each
other at all times. Reposition head B as appropriate to
maintain this orientation.
NOTE
At the start of each path the level must be adjusted for 0 reading.
(5) Lay straight edge immediately adjacent to line that is to be calibrated northwest
to southeast and clamp to TI.
(6) Position head A adjacent to straight edge at first station to be measured.
Head B will remain stationary.
14