Present methods of linear measurement in micro-surgical procedures in the middle ear are crude when judged in relation to the delicate structure and functioning of the normal ear.

Alternative methods of measurement employing the operating microscope are described. These depend on recording the travel of the microscope between two selected focal points and can be employed in both vertical and horizontal planes. Oblique distances can readily be calculated from the information provided. Minor alterations to existing microscopes would be required to ensure precise recording bv electronic or linear methods.