The heart of the Variable Scale is a high precision triangular spring
whose coils act as calibrating lines. When extended, all coils are
equally spaced. A second spring carries numerical markings for each
10th coil of the triangular spring.
Easy to use, the Variable Scale makes computations directly -- without
conversion -- on graphs, curves and recordings. Expandable for any ratio,
any setting, it is used on graphical work where reading, plotting and
interpolating are required.
The use extends the Variable Scale's springs by sliding a hairline over
three fixed, engraved scales: 1) an Inch scale that indicates the number
of inches extended; 2) a Reciprocal scale that identifies the number of
coils per inch; and 3) a Logarithmic scale that indicates the logarithm
of the extension. Each scale, in combination with the spring, solves a
group of common problems.