THE recent introduction of the “Watts” jig borer microscope provides a valuable optical accessory for use with high-precision machine tools such as jig borers, and tool-room milling machines, Its purpose is to enable the axis of the machine to be accurately located in relation to a datum mark on the work-piece. In construction, it consists of a high-power microscope the optical path of which is bent so that the user can conveniently inspect the work from one side when the instrument is set up in the spindle of the machine. The microscope is mounted on a taper shank-No. 4 morse taper is used in the standard model but any of the usual tapers can be supplied- and the shank is inserted in the spindle. In this position the objective axis of the microscope coincides with that of the boring spindle, which the operator is thus enabled to bring within an accuracy of 0 -00005 in. to the desired position.