Chapter 6  Building Layout
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6.5 Using the
Instruments
A carpenter can use leveling instruments
to prepare the building site for excavation
and grade leveling. Jobs that can be done with
leveling instruments include:
• Locating the building lines and laying out
horizontal angles (square corners).
• Finding grade levels and elevations.
• Determining plumb (vertical) lines.
For layout, the builder’s level or transit must
start from a reference point. This can be a stone
marker in the ground, point on a manhole cover,
or mark on a permanent structure nearby. The
point where the instrument is located is called
the station mark. It may be the benchmark, the
corner of the property, or a previously marked
point that is to be a corner of the building. This
might be a stake with a nail in it or the intersec-
tion of two string lines marking the corner of a
building line.
6.5.1 The Horizontal
Graduated Circle
Laying out corners with the transit requires
an understanding of how the horizontal gradu-
ated circle is marked. It is divided into spaces of
1°, Figure 6-13. When you swing (rotate) the tele-
scope of the builder’s level or transit, the gradu-
ated circle remains stationary, but another scale,
called the vernier scale, moves. It is marked
off in 15-minute intervals. When laying out or
measuring angles where there are fractions of
degrees involved, you will use this vernier scale.
Figure 6-14A shows a section of the gradu-
ated circle and the scale. It reads 75°. Notice that
the zero mark on the vernier exactly lines up
with the 75° mark. Now look at Figure 6-14B.
The zero mark has moved past the mark for
75°, but is not on 76°. You need to read along
the vernier scale until you find a mark that is
closest to being directly over a degree mark on
Station mark:  The reference point where a builder’s
level or transit is set up when laying out building lines
or finding grade levels and elevations. It must be a type
of marker that will not be disturbed by any construc-
tion activity.
Benchmark:  A mark on a permanent object fixed to
the ground from which grade levels and elevations are
taken for construction of a building. Sometimes offi-
cially established by government survey.
Vernier scale:  Device on a transit that measures
minute portions of an angle.
270° 90°
180°
360°
45°
1°
Measurements of a circle
Circle
1°
1 minute
1 quadrant
= 360°
= 60 minutes
= 60 seconds
= 1/4 circle or 90°
90° = square corner
= 1 quadrant
Figure 6-13. The graduated circle of a transit corre-
sponds to the 360° of a full circle; 90° represents a
quadrant, which would give you a square corner for a
building.
Crosshairs
3
A B
Figure 6-12. View through the telescope. A—Cross-
hairs vertically and horizontally split the image area in
half. B—The object in the view should be centered on
the crosshairs.