The cameras metering system only sees an average number, which is 18% grey.
Point it at a white wall and you'll need to over expose by two stops.
Point it at a black wall you will need to under expose by 2 stops.
When you point your camera at a scene the camera will base the exposure on an 18% grey average.
This is really base level photography 101. Read up on it.
I know how a camera's meter works. And to return the condescension:
Point it at a white wall, and you'll need to overexpose by two stops to make it white
Point it at a black wall, and you'll need to underexpose by two stops to make it black
I was talking about making that blank wall, whatever its tonality, a middle grey. If you'll read my posts rather than feeling self-important, you'll see that I understand that no matter what the tonality of the blank wall you point it at, the meter should render it 18% grey, i.e., middle grey. So I was expecting a centered histogram when shooting at the meter's reading. And I was getting a histogram that was about a stop below the center. Thus my assertion that the meter was underexposing.
Why don't you take a look at my work, and then we can discuss again whether I should read up on photography 101. www.ethanpines.com