Sometimes the most obvious feature of a tool has nothing to
do with its intended use. During the manufacturing process,
reworks of the original concept can alter the tool's performance
or indicate a different function. This tool is quirky in that
its form can lead one to misread its capabilities.
In patent #521,414, granted in 1894, Joseph T. Langlais of Berkeley,
California, sought to improve the measuring and marking of angles
by introducing a different style of gauge compared to existing
single-leg bevel gauges. The tool's two arms, or handles, are
used to replicate or record any angle. The arm-fixing
mechanisms are locked into the desired angle by pushing down
on the two levers. To release them, you simply lift up.
By virtue of the gear arrangement on the arms and the blade
that joins the two arms together, they always work in concert.
The blade, however, gives the impression that this tool can
be used in a much different manner. When the gauge is opened,
one would think the metal leg can be used to bisect an angle
because the blade is always centered. (The bisector of an angle
is the line or line segment that divides the angle into two
equal parts.) This is not the case. The width of this connecting
blade (used in the construction of the bevel) has no provision
or markings to indicate the bisector. This gauge can do only
one thing — replicate or indicate an angle, as stated
in the patent.