Metering depends on the built-in light meter of the camera. Built-in light meters use the reflected light meter technique to meter for the ambient brightness. This is not the most accurate of ways to meter for a scene. That said hand-held light meters are the most reliable. This is because these meters use incident light for metering a scene. This is a much more accurate way to meter.
Metering will also depend on the metering mode of the camera that has been selected. This will determine how much of the scene will be used for metering purposes. There are a total of three different types of metering modes – matrix, spot and center-weighted.
Canon systems have a fourth metering mode known as partial metering.