This is what your vernier looks like after having turned the angle (Fig. 12). Now, let's
read the angle. Remember, we have turned to the left, so we are going to use the
side of the vernier between the vernier index "V" and the letter "L".
NOTE: Do not be confused that the positions of "L" and "R" are reversed.
Observe in this case that the vernier index has passed the 44 degree line on the circle
but has not gone as far as the 45 degree line. Right away, we know that the angle we
have turned is greater than 44 degrees but not much greater than 44 degrees.
In the example we have chosen, we must add to 44 degrees the reading obtained
from one of the vernier lines. Which vernier line? You will see that the fourth line
from the vernier index is lined up with one of the lines on the circle (Fig. 13). This is
the secret of the vernier. Only one line at a time can be lined up. Since in this case it
is the fourth line from the index, we will add 20 minutes to the 44 degree reading (4
times 5 minutes equals 20 minutes). Therefore, our exact reading is 44 degrees 20
minutes (44° 20').
Other instruments have a vernier reading to 15 minutes (1/4 degree) and will look like
the illustration below:
Whether reading this vernier or the one shown on page 10, the principle is the same.
The only difference is that each line on the vernier represents 15 minutes (1/4
degree) instead of 5 minutes.
Notice in the above illustration that the index has passed the 44 degree line but has
not gone as far as the 45 degree line. In this case the third vernier line from the
index is lined up with one of the lines on the circle. Since each vernier line represents
15 minutes, add 45 minutes to the 44 degree reading (3 times 15 minutes equals 45
minutes). Therefore, our exact reading is 44 degrees, 45 minutes (44° 45').
8.2 THE VERTICAL VERNIER
In reading the vertical vernier (if instrument is so equipped), the principle is exactly
the same as the horizontal vernier. Note, however, that the vernier is below (or
outside) the circle portion rather than inside as in the case of the horizontal. One
other minor difference is that you will read angles up or down rather than left or right.
Here again we have a double vernier. The right hand side reads angles of elevation
(up) and the left hand side reads angles of declination (down). These are the only
differences between the horizontal and vertical verniers.
Berger Instruments • 11
As described in the chapter “Measuring Horizontal Angles”, center and level your
instrument over point I. Sight the telescope on point H and set the horizontal circle
to read 0°. Loosen the horizontal clamp and rotate the telescope until the index
pointer is very close to 90°. Tighten the horizontal clamp and turn the horizontal
tangent screw until the index reads exactly 90°. The line of sight (vertical crosshair)
will indicate point J and all you have to do is to set J along the line of sight by taping
the required distance from I.
8. READING THE VERNIER
8.1 The Horizontal Vernier
Reading a vernier is a simple process as you will see from the following:
Your vernier is actually a double vernier, that is, two verniers in one. This makes it
possible to read any angle turned by the telescope, whether to the right or to the
left. For example, consider that you have turned an angle to the left
(counterclockwise) after first having set the circle to read 0° (Fig. 11).
10 • Berger Instruments
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