How does Nikon D5000 measure white balance with gray card?

The method of measuring white balance with gray card in Nikon D5000;

1. Select "Manual preset" in the white balance menu, and then select "Measure";

2. There will be a flashing "Pre" on the focus screen, and then the gray card will stand next to the subject;

3. Shoot at the gray card (be sure to fill the picture with gray cards). After the photo is taken, the camera will not save the photo, but only measure it. After the measurement is completed, you can take pictures.