[wiltw]

Forget about "calibrating (TTL) meter". Your first priority is to load transparency film into the camera and shoot as the meter reads the scene: leave it all to the TTL meter to start with. .

...but never forget the phenomenon of 'subject failure'...a metering target which fails to match the assumption of average brightness of 18% gray. Even TTL meters cannot remain immune to subject brightness induced metering error!