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Decimal Vernier Graduation.
For railroad work it is sometimes requested to graduate vernier A to read to
minutes or 30", as usual, and vernier B to read to T pth of a degree.
If the circle is to read to minutes, vernier A will be as shown in figure 1. A
decimal vernier for this graduation requires 49 spaces of the circle to be divided into
50 parts on the vernier, making a very long vernier, so that there is only room for a
single vernier in the opening of the vernier plate. This vernier would either have two
zero points as in figure 4, or would have the zero at the center, as shown in figure 6.
If one vernier is to read to 30" and the other to T^th of a degree, the circle would
be divided into 15' spaces, and the A vernier would be as shown in figure 9. The
decimal vernier for this graduation requires 24 spaces of the circle to be divided into 25
parts on the vernier as shown in figure 8.
The disadvantages of such graduations are, first, that the spacing of the circle is too
doss for rapid reading, and second, that mistakes are liable to be made in reading the
verniers by confusing the 30" reading of vernier A with the T^th of a degree of
vernier B. Another disadvantage is that when it is desired to read both verniers,
A and B, as in repeating angles, this cannot be conveniently done with either of the
above arrangements. For these reasons the two verniers A and B, should have the
same graduation.
There are occasionally inquiries for transits provided with decimal vernier graduation.
These can be furnished when desired, but must be specially made to order. On
account of the great length of the double vernier, single opposite verniers of the folding
pattern (fig. 6) are the only feasible ones. Although objections are often raised
against them, still many engineers like folding verniers after becoming accustomed to
them.
Decimal Vernier Graduation.
r. 8. Circle divided into 15' spaces.
Double vernier (24 spaces into 25) reading to hundredths of a degree.
Graduation Heading to 3D".
On same limb with B vernier to read to lOOths of a degree as in Fig. 8, and A vernier
reading to 30".
8.
360
Fig. 9.
. 9. Circle divided into 15' spaces.
Double vernier A (29 spaces into 30) reading to 30".
of a degree.
This vernier is not commonly used, but has the advantage
occupies only a short space.
10
B vernier reading to lOOtns
that the double vernier