A highly sensitive variable resistor that transforms slight mechanical displacements into large changes in electrical resistance, current, or voltage, has been developed under the direction of W. A. Wildhack at the National Bureau of Standards. A conical spring is wound with variable tension so that its turns separate one by one rather than simultaneously and as a result its electrical resistance varies from that of a cylindrical tube to that of the total length of the uncoiled wire. Thus displacements as small as a hundred‐thousandth of an inch can be measured without using an electrical amplifying device.

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