Abstract: The invention relates to the field of frequency measuring, in particular to extremely accurate difference frequency measuring as it is used in the area of measuring instruments, e.g. in scanning atomic force microscopes or other scanning probe microscopes, or in the area of thermogravimetry for determining extremely small masses in the ng-range. The invention relates in particular to the principle of such a hybrid frequency measuring device or frequency detector, i.e. a frequency measuring device or frequency detector comprising both digital and analog components or groups of components. The invention also relates to an advantageous use of such a frequency detector for evaluation of the frequency measurements of a scanning probe microscope. A frequency measuring arrangement can be at least partly integrated in a measuring head of a scanning probe microscope, thus enabling a robust, and at the same time sensitive, measuring arrangement.