Profiles constructed graphically from topographic maps are time-consuming
to prepare and do not show details or breaks in slope that have relief
less than the contour interval. It is also time-consuming to collect the
field data needed for construction of profiles because numerous altitude
measurements must be made along any one line of traverse in order to
show minor breaks in slope. With an exaggerated profile plotter,
vertically enlarged cross sections of terrain can be drawn rapidly.
The combined use of field measured stratigraphic sections and
vertically enlarged profiles drawn from aerial photographs with the
exaggerated profile plotter has proved to be an efficient and reliable
method of stratigraphic and structural study in the Black Hills.
The instrument is essentially a vertical pantograph that applies the
principle of proportional triangles to a lever and fulcrum system. It
consists of the following parts (the relation of each part to the whole
instrument is shown in figure 2): base plate and track bearing; fulcrum
bar; vertical track bar; sliding-unit assembly with spring loaded pencil;
tracing arm bar; and pivot point stud (attaches to tracing table). A
metal track at the base of the plotting board guides the track-bearing
assembly along the line of profile. As the carriage of the tracing
table is moved up and down, the sliding-unit assembly moves a proportion-
ately greater distance. The enlargement ratio varies with the distance
from the fulcrum to the pivot point. The instrument shown in the
figures is designed for 132, 1:3, or 1:5 times enlargement; it could be
modified for other ratios ranging from 1:1.5 to 1:6. The spring loaded
pencil produces a clear legible line; fine-line ballpoint pens are
acceptable also. The instrument can be used with any of the double-