This section is from the book "The Manufacture Of Boots And Shoes: Being A Modern Treatise Of All The Processes Of Making And Manufacturing Footgear", by F. Y. Golding. Also available from Amazon: The Manufacture Of Boots And Shoes.
It was formerly considered that the cutting of an elastic-side pattern was an easy task, requiring little skill; but it is a pattern that well pays careful attention. The amount of the elasticity of the web to be used should come in for consideration, so that proper provision may be made for the width of the gusset, thus preventing the ingress and egress of the foot during use having too great a demand upon the elastic strands. The curve at the throat of the pattern must be easy and not made to resemble the pattern prevalent for lace boots. The lower curve of the gore or gusset should come below the line of the heel-measure, and be pitched forward, similar to the line ab, Fig. 129. This will enable the strands of the rubber to lie in the direction of the strain that falls upon the web during the putting on and off of the boot. The front line of the spring should be at right angles with the top line of the gore. Assuming the standard from which an elastic-side pattern is to be cut correctly fits the foot, to make it adaptable to the requirements of an elastic side, one-ninth of an inch should be taken from the top, back and front, reducing it in measurement, giving the web an opportunity to exert its property. The principles of designing may be obtained by reference to p. 178 and Fig. 146.