A method and apparatus for interfacing a plurality of gas measurement systems,
including a mainstream and a sidestream gas measurement system, to a host system
via an interface unit. The present invention also pertains to a sidestream gas
measurement system that output signals emulating the signals output by a mainstream
gas measurement system or portion thereof, so that the sidestream gas measurement
system can seamlessly communicate with a host system configured to communicate
only a mainstream gas measurement system or a portion thereof.