How to Make an Enlarging Chart – Most boys like to do some drawing occasionally and very often this means making an enlargement and a reduction in the overall size that can be most difficult to work out. The chart illustrated will show you the exact figure at a glance.
The chart involves the diagonal method of enlarging or reducing and you have probably been taught how to use at school. Supposing you have an oblong measuring 6 in. wide by 2 in. deep, and wish to enlarge this so that the width becomes 9 in., you will want to know the depth. The diagonal method means drawing out the oblong and then running a diagonal line through the corners A, as illustrated. Mark 9 in. along the top line and run a vertical line downwards, until it touches the diagonal line. Now measure along to this point, in a vertical direction and you will find the depth. For reducing, the process is the same. You mark along the top line the size to be reduced and run a vertical line down to the diagonal line and measure the distance. The answer will be shown quite clearly.
The chart illustrated here does away with all the drawing and yet includes the diagonal principle. The black cotton represents the diagonal line and is moved by hand to exactly the position of where the points of the oblong meet. The enlargement or reduction can be read out quite easily by just looking at the black thread and noting the horizontal and vertical measurements.
The chart is quite simple to make. Obtain a piece of white drawing board about I0 in. square and rule a pencil line across the top of this, I in. from the edge. Now rule a further pencil line I in. from the left hand side of the card. Mark I in. spaces along the top and side and complete the squares, so that you will now have a square 8 in. by 8 in. The next step is to subdivide the squares into 1/8 in., as illustrated. You will now have an 8 in. squared chart, with each I in. square containing 1/8 in. squares.
Make a hole with a pin at point A and thread a piece of strong black thread through this and tie on to a piece of short wire or paper clip, as illustrated. Gum a piece of sticky paper over this thread knot and the wire, so that it will be held securely in place. Now mark the inches along the top and down the side of your squares and the chart is ready for use. Hold the chart in the left hand and find the point where the corners of your oblong meet, run the cotton over this point and you will be able to find the enlargement or reduction along the black line.
To give longer life to this very useful chart, paint the surface all over with artist’s varnish and allow to dry before using.