Abstract: Disclosed is a two-coordinate measuring device for use in the measuring ocular of a microscopic measuring instrument, comprising at least one reference mark carrier movably mounted in an intermediate image plane of the instrument and having a direction of movement which forms an angle of 45.degree. with axes in the x- and y-direction defined by the object, and means mounted in the measuring ocular for adjusting the position of the mark carrier in order to align the reference mark with the dimensions of an object which is to be measured. The reference mark of the carrier preferably comprises two perpendicular lines which are arranged on the carrier such that the bisector of the angle formed by the lines coincides with the direction of movement of the carrier. Also disclosed is a process for use of this device.