In the figure, shutter speeds are indicated at the left with the number from 0 to 9, and the aperture at the right from 4 to 9.
To get a correct exposure, coincide the sum of each number with the light value number.

Ex. Exposure meter indicates 13 and the aperture number is now 5. And so, the shutter speed number that has to be set to get a correct exposure is 8.