http://www.knoxvilleobservers.org/ds...ps/telrad.html
It does becomes more intuitive when you have one to look at .
the circles themselves are are good guage for distance break them down again to a clock face .
An easy example the blue planetary (ngc 3918)
project a line from Beta to Delta crux, place the outer telrad circle
9 oclock on delta crux .. your centre dot is on a line now .
beta , delta, 9 oclock.. but the object is another half degree or so further out on this line so you have to nudge it out just a little more
. It can't hide for long
.
