Abstract: Apparatus for measuring pressure on a well drilling bit which bit is connected to the drilling platform at the surface by a string of drill pipe, typically in a slant drilling configuration. The apparatus is inserted in the drill string and includes first and second sections of drill pipe with telescoping ends and a spring positioned therebetween urging one section away from the other. A radioactive source is mounted in one of the sections and a probe carrying a radioactive detector is positioned within the drill pipe, with a window in the other section of pipe providing a radiation path between the source and detector. Pressure on the drill bit varies the compression force on the spring permitting one section of pipe to move relative to the other and thereby vary the position of the window in the path between the radiation source and detector. The output of the detector varies as a function of window position and hence as a function of pressure on the drilling bit.