Spherometer

A contact-lever, delicate level or electric contact may be attached to the spherometer in order to indicate the moment at which the four points exert equal pressure.

To do so, the instrument is placed on a perfectly level plane surface and the screw turned until the point just touches; the exact instant when it does so is defined by a sudden diminution of resistance followed by a considerable increase.

[2] Tool pipe with thicker than 1" walls for a 4" diameter tube of hardened steel, fitted with tapered thread collars, are re-used after drilling is complete and thinner-walled tubular oil-well casing is in place.

Electronic instruments similar to the spherometer in design are used at inspection plants for casing, tubing, and drill pipe.

A related device is the cylindrometer (also known as cylindro-spherometer or sphero-cylindrometer), which can additionally measure the radius of curvature of a right-circular cylinder.