Reading
given
upon the
Scales.		Reduces
in the
Proportion
of
1—21to 2
1—31„ 3
1—41„ 4
1—51„ 5
1—61„ 6
1—71„ 7
1—81„ 8
1—91„ 9
1—101„10
1—111„11
2—32„ 5
3—43„ 7
4—54„ 9
5—65„11
6—76„13
7—87„15
8—98„17
9—109„19
10—1110„21
11—1211„23

“In the above Table the readings which are given with the proportions are given to show clearly which proportions agree with the erect scales; many of those that do not agree with the reading are very useful, as 2—3, which is often required to reduce a drawing from a scale of 20 to one of 50.

“In the reverse manner of setting the pantograph, the reduced copy appears reversed, or upside down, to the original. The fulcrum pin is placed in the socket upon the short central rule, and the pencil holder is placed in the socket upon the outside rule. This is generally the most convenient way of using the pantograph for large drawings, as the original and copy come edge to edge, and need not overlap each other, which is often compulsory in the erect manner; the range of scale is also much greater, as the proportions include the unit proportions of the erect scale, and continue in ratios up to full size.

“The following Table will give the readings of the instrument which accord with the reverse setting, and those which may be used to this setting, obtained by calculation.

Table of Reductions by the Pantograph in the Reverse manner, the Fulcrum being placed in the Socket on the Central Rule, and the Pencil in the Socket upon the Outside Rule.

Reading
given upon
the Scales.		Reduces
in the
Proportion
of
1—21to 1 full size
1—31„ 2
1—41„ 3
1—51„ 4
1—61„ 5
1—71„ 6
1—81„ 7
1—91„ 8
1—101„ 9
1—111„10
2—32„ 3
3—43„ 4
4—54„ 5
5—65„ 6
6—76„ 7
7—87„ 8
8—98„ 9
9—109„10
10—1110„11
11—1211„12

“The above Table and the previous one give the proportions for reductions, the tracing point being in every instance considered upon the outside rule. If it were required to produce an enlarged copy, which the pantograph will do but very imperfectly, the pencil and tracer would have to change places; the proportions of course would read the same.

“In using the pantograph some care is required in setting the fulcrum weight in the best position to allow easy action of the instrument over the space required. It should always be roughly tried over the boundary before commencing the copy.

“The ordinary pantograph will in no instance work over a large drawing at one operation, but it may be shifted about as required, using care, and testing the copy after the fulcrum is moved, to see that the tracer and pencil correspond in those parts already produced, that the pantograph will reach in its shifted position. The fulcrum weight being generally made with needle points to attach it to the drawing will be found very difficult to shift so short a distance as is frequently required. This may be easily remedied by attaching with gum a piece of indiarubber over each of the sharp points, when it is required to be used for large drawings. The rubber will hold the paper sufficiently if the pantograph work freely in the joints and casters, as it should do.

“In copying the buildings which frequently occur in plans of estates, &c., a straight slip of transparent horn will be found very convenient to guide the tracing point. Some draughtsmen have the horn cut with an internal angle, by which one side and one end of a building may be traced without shifting the horn.