Confidence in a physiological parameter is measured from physiological data responsive to the intensity of multiple wavelengths of optical radiation after tissue attenuation. The physiological parameter is estimated based upon the physiological data. Reference data clusters are stored according to known values of the physiological parameter. At least one of the data clusters is selected according to the estimated physiological parameter. The confidence measure is determined from a comparison of the selected data clusters and the physiological data.

A medical instrument comprises an interface for electrically connecting a drive unit with the medical instrument. The interface has a plurality of electrical contacts arranged in a connecting surface. At least one of the contacts in the connecting surface is electrically isolated from the remaining contacts by a recess or an elevation.