Abstract: An apparatus for use in determining the location of a surface of a solid object such as that being machined by a machine tool includes a stylus having an electrically conductive end that is supported by two support members, which are disposed in pressure contact with each other by means of a spring or other bias, one of the two support members being formed to have a spherical contact surface that is a portion of an imaginary sphere concentric with the contact electrode, the other of the two support members being formed so that upon contacting the spherical surface the area of contact is substantially line contact.