Abstract: An interface unit for receiving a body part of a subject at which a noninvasive hematocrit measurement is to be obtained includes a narrow monitoring element with a receptacle for receiving at least a portion of the body part and contacts that are configured for establishing electrical communication with contacts of electrodes that are to be positioned over the receptacle before the body part is placed therein. In addition, the monitoring element may include a pressure port that communicates pressure into the receptacle. The interface unit also includes a cover which is configured to partially enclose the body part, to ensure that electrical communication is established between the contacts and the electrodes, and to facilitate the application of pressure to the body part. The electrodes may be in the form of electrically isolated electrode pairs, which may be formed as a strip with minimal material wastage.

Abstract: Apparatus and method are provided for calibrating a mass spectrometer. The calibration hardware includes a relatively small, relatively low pressurized tank for containing calibration gas. The calibration gas tank is preferably located inside the same housing that contains the ion source assembly and the analyzing section of the mass spectrometer. Each of the calibration gas and sample gas, whose components are to be determined, communicates with its own associated valve. These two valves control the flow of a selected one of the sample gas and the calibration gas to the ion source assembly. The calibration gas valve has an extremely low leakage rate and can be controlled to permit the passage of very low flow rates of calibration gas, which can be of benefit in checking the linearity associated with the ion source assembly pressure. For each calibration procedure, very small amounts of calibration gas are utilized, in a range around 10.sup.-5 STD cc.