A Practical Demonstration

If your camera has a live view LCD screen, you can try this:

If you can, and normally you can, set the screen to monochrome

Set the metering mode to either center weighted or the camera’s default mode

Find a scene with a wide tonal variation—indoors is best, a room on a sunny day is ideal

Slowly pan the camera while watching the

LCD screen

Now set the metering mode to spot, and pan the camera over the same scene while watching the LCD screen

This is what should have happened:

On the first setting, the brightness of the image on the LCD screen changed gradually, if at all

On the spot setting, the changes should have been much more dramatic, going from very light to very dark and back again, with very little movement of the camera