175
The accuracy of the circle graduation.
When a discussion of the instrumental merits of the radial-triangula-
tor is wanted, it is unelegant to determine, as Schubert has done in
-by
23
errors in dmgr
Fig. 7
his paper, the mean error in the measurement of a direction caused
by the sum of the errors in the setting of the measuring mark and the
reading of the verniers. The
first mentioned source of
errors depends among other
things on the quality of the
photograph and the visual
acuity of the observer and
is-therefore independent of
the instrument. The resol
ving power of the optical
parts of the instrument has
generally a secundary in
fluence.
We are, for our purpose,
interested in the mean error
of the reading of the circle
9 X
5 X
-A
/o o\
X Ri
\2 Rz
9 X -
5 X
errors in dmgr resp mm
Fig. 8
and in the influence of errors in the circle graduation.
Both errors were determined by a method that is schematically
indicated in fig. g. A theodolite T
was placed on the plate-carrier so
that the first axis corresponds as
good as possible with the rota
tion axis of this carrier. To avoid
secundary influences both axis
were carefully verticalized.
The theodolite was pointed to
a collimator C. After rotating the
plate-carrier each time over 5 gra
des the theodolite was anew
■plate-carrier
pointed to C and both circles were read. Since the reading of the
theodolite could be considered errorless (mean error ca 2 dmgr) with
3
+22
Li\
R1
-55\
+3
Fig. 6
+10
-6
yi \fi
V
/o 0
0\
-10 +6
Fig. 9
