There is a choice of two apertures for automatic flash photography. They are indicated by the two color-coded indices above the aperture scale. The apertures to which these indices point change with film speed. As ASA 100 for instance the green index points to f/5.6 and the red index to f/2.8

To set one of there apertures on the flash, simply switch the aperture selection switch to one of the "A" positions so that red or green appears in the aperture selection window. The colors of these "A" positions correspond to the colors of the aperture indices. If for instance you set the switch to the "A" position which causes green to appear in the aperture selection window, you are regulating the flash to the aperture pointed to by the green aperture index. The aperture selection switch also has an "M" position which corresponds to the color white in the aperture selection window. For automatic flash, this setting should be ignored: if is for manual flash shooting.