On Thu, 24 Mar 2005 02:33:44 GMT, Erik wrote:

In article ,
"R.H." wrote:

http://puzzlephotos.blogspot.com/

I actually have a #303... Saw it at a tool swap meet a while back, and
was playing with it. Asked the owner what it was. Said he hadn't a clue,
but it was mine for 50 cents.

I suspect it's some sort of survey equipment. Know for sure it was a
good bit over 50 cents new.

Erik
It is called a right angle prism and is used to find the point on a
line from which a perpendicular line may be run to another point, then
the true distance from the line to the point may be measured. this
information can be very important particularly in property surveys. In
use, a plumb-bob is suspended from the "handle" such that it is just
clear of the ground, the point is viewed through centre plain glass
section and lined up with markers on the line viewed through the upper
and lower penta-prisms, when the point is on line the plumb-bob is
lowered to mark the required point on the line.
Alternately, the prism is also used to project perpendicular lines
from points along a base line to enable accurate quantity measurement.
See:

http://www.fao.org/docrep/R7021E/r70...tic%20sq uare

Gerry :-)}
London, Canada