This is a wonderfull jewel ! It is a calculator that actually takes all that is important for average conditions photography and put it in a playfull and funny way.
You start always at the same point with the dial and then, in that order, you dial according to:
1- Your subject: well lit indoors, far landscapes, buildings, groups etc
2- Sky conditions: open sun, overcasted, etc
3- Film Sensibility
4- Month and hour.
That is it. You can read the pairs speed and apperture now. I find ingenious to introduce the month and hour to get the light conditions. Of course it works only in a certain latitude (for France this one ?) but it is really nice. After ringing and ringing it stops on the right spot !