To help you determine whether the exposure settings on your Nikon D7000 are on cue in M (manual) exposure mode, the camera displays an exposure meter in the viewfinder and Information display. The meter is the little linear graphic, and you can see a close-up look at how it looks in the viewfinder. To activate the meter displays, just press the shutter button halfway and then release it.
The minus-sign end of the meter represents underexposure; the plus sign, overexposure. So if the little notches on the meter fall to the right of 0, the image will be underexposed. If the indicator moves to the left of 0, the image will be overexposed. The farther the indicator moves toward the plus or minus sign, the greater the potential problem. When the meter shows a balanced exposure, you’re good to go.
In the other exposure modes, the meter appears if the camera anticipates an exposure problem. The word Lo at the end of the meter tells you that the photo may be seriously underexposed; the word Hi indicates severe overexposure. In dim lighting, you may also see a blinking flash symbol. It's a not-so-subtle suggestion to add some light to the scene. (You can disable the flash alert through the Flash Warning option on the Custom Setting menu if you like.)
Keep in mind, too, that the meter’s suggestion on exposure may not always be the one you want to follow. For example, you may want to shoot a backlit subject in silhouette, in which case you want that subject to be underexposed. In other words, the meter is a guide, not a dictator. In addition, remember that the exposure information the meter reports is based on the exposure metering mode, which determines which part of the frame the camera considers when calculating exposure. At the default setting, exposure is based on the entire frame, but you can select two other metering modes.
If you’re so inclined, you can customize the meter in the following ways:
Adjust the meter shutoff timing. The meter turns on anytime you press the shutter button halfway. But then it turns off automatically if you don't press the button again for a period of time. You can adjust the shut-off timing through the Auto Meter-Off Delay option, found on the Timers/AE Lock submenu of the Custom Setting menu. Choices range from 4 seconds to 30 minutes. You can also disable the auto meter shutdown by choosing the No Limit option, but remember that the metering system uses battery power, so keeping it active for long periods of time on a regular basis isn't a good move.
Reverse the meter orientation. For photographers used to a camera that orients the meter with the positive (overexposure) side appearing on the right and the negative (underexposure) side on the left, the D7000 offers the option to flip the meter to that design. This option also lies on the Custom Setting menu, but on the Controls submenu. Look for the Reverse Indicators option.