Congratulations on the purchase. The meter is a (kind a of) centre-weighted system and is pretty accurate for most situations. However, as with most cameras, one has to compensate for strongly back-lit situations or if the picture is far removed from an average 18% grey scene. The handy dial at the back allows upto +/- 2 stops compensation. The manual says the following.....
A light metering sensor located to the side of the viewfinder objective
lens measures the photographing area in five independent segments
and calculates the correct exposure by a center-weighted multiple-
field comparative algorithm.The metering system calculates the
correct exposure based on the lens's photographing field, the brightness level of the photographic subject, the contrast among metering segments and miscellaneous factors to achieve the best photographic image reproduction. Refer to 6. References (Exposure
Measurement Sensitivity Patterns).
Note 1: The impact on exposure settings of any filters attached to the lens must be taken into consideration to determine the correct exposure when compensation for the exposure determined by the external metering system of the Bronica RF 645.
Note 2: The metering range of the Bronica RF 645 is from EV 3 to EV 18 with the 65mm standard lens at ISO 100. EV 3 (at ISO 100) is an exposure level designated by a combination of f/4 aperture and 2 second shutter speed. EV 18 (at ISO 100) is an exposure level designated by a combination of f/22 aperture and 1/500 sec. shutter speed.
Note 3: EV level varies when any film speed other than ISO 100 is used, or exposure compensation is applied.
If you didn't receive a manual with your camera, a pdf can be obtained from...
All the best.