durability. Standard lengths are 50 and 100 ft.
Some are graduated in feet and inches to the
nearest one-fourth in. Others are graduated in feet
and decimals of a foot to the nearest 0.05 ft.
Metallic tapes are generally used for rough
measurements, such as cross-sectional work,
road-work slope staking, side shots in topographic
surveys, and many others in the same category.
Nonmetallic tapes woven from synthetic yarn,
such as nylon, and coated with plastic are
available; some surveyors prefer to use tapes of
this type. Nonmetallic tapes are of special value
to power and utility field personnel, especially
when they are working in the vicinity of high-
voltage circuits.
Steel Tapes
For direct linear measurements of ordinary or
more accurate precision, a steel tape is required.
The most commonly used length is 100 ft, but
tapes are also available in 50-, 200-, 300-, and
500-ft lengths. All tapes except the 500-ft one are
band-types, the common band widths being 1/4
and 5/16 in. The 500-ft tape is usually a flat-wire
type.
Most steel tapes are graduated in feet and
decimals of feet, but some are graduated in feet
and inches, meters, Gunter’s links, and chains or
other linear units. From now on, when we discuss
a tape, we will be talking about one that is
graduated in feet and decimals of a foot unless
we state otherwise.
Some tapes called engineer’s or direct reading
tapes are graduated throughout in subdivisions
of each foot. The tape most commonly used,
however, is the so-called chain tape, on which only
the first foot at the zero end of the tape is
graduated in subdivisions, the main body of the
tape being graduated only at every 1-ft mark.
A steel tape is sometimes equipped with a reel
on which the tape can be wound. A tape can be,
and often is, detached from the reel, however, for
more convenient use in taping.
Various types of surveying tapes are shown in
figure 11-36. View A shows a metallic tape; view
B, a steel tape on an open reel; view C, a steel
tape or, a closed reel. View D shows a special type
of low-expansion steel tape used in high-order
work; it is generally called an Invar tape or Lovar
tape.
Invar Tapes
Nickel-steel alloy tapes, known as Invar,
Nilvar, or Lovar, have a coefficient of thermal
Figure 11-36.-Surveying tapes.
expansion of about one-tenth to one-thirtieth (as
low as 0.0000002 per 10F) that of steel. These
tapes are used primarily in high-precision taping.
These tapes must be handled in exactly the same
manner as other precise surveying instruments.
The alloy metal is relatively soft and can be easily
broken or kinked if mishandled. Ordinarily, Invar
tapes should not be used when a steel tape can
give the desired accuracy under the same operating
conditions. Invar tapes are used for very precise
measurements, such as those for base lines and
in city work. When not in use, the tape should
be stored in a reel, as shown in figure 11-36, view
D. Except for special locations where the ground
surface is hard and flat, such as roadways or
railroads beds, the Invar tape is used over special
supports or stools and is not permitted to touch
the ground.
SURVEYING ACCESSORIES
Surveying accessories include the equipment,
tools, and other devices used in surveying that are
not considered to be an integral part of the
surveying instrument itself. They come as separate
items; thus, they are ordered separately through
the Navy supply system.
When you run a traverse, for example, your
primary instruments may be the transit and the
steel tape. The accessories you need to do the
actual measurement will be the following: a tripod
to support the transit; a range pole to sight on
in line; a plumb bob to center the instrument on
the point; perhaps tape supports if the survey is
of high precision; and so forth. It is important
that you become familiar with the proper care of
this equipment and use it properly.
11-37
