A correspondent writing in the "Morning Post' says One is disposed to regard machines for measuring to one ten-thousandth of an inch as being the acme of complexity, so it is somewhat surprising to learn that the latest development in the science of metrology is nothing more than an ingenious adaptation of the familiar lantern slide projector.
For modern quantity production of machine parts accurate gauges are essential, and particularly screw gauges. To check precision screw gauges itis necessary to have the means of measuring the effective diameter, the distance apart between successive threads, and the form of these threads to within two or three ten-thousandths of an inch.
To do this mechanically is a laborious procedure owing to the numerous point by point readings which have to be taken. The task has been enormously: simplified by a simple machine devised by the National Physical Laboratory, in which a silhouette of the screw is projected on to a screen. A magnification of exactly 50 times is employed. The observer has before him a complete outline view of the gauge, the threads appearing like saw teeth.
Text read from the printed page and cleaned; old type leaves the occasional error.