You've been exposed!
I inherited this exposure calculator from my dad (a keen amateur photographer himself) - he first got his in the 1950s. The calculators helped you work out the aperture and shutter speed according to the subject and conditions you were shooting in. I am pleased I didn't have to learn the technical aspects on this but I am pleased that I learnt to take photographs on a SLR as it made it think about aperture and shutter speed and have a better understanding of photography. These days it's all very easy (how many people do not take their cameras off automatic?) and whilst I have embraced digital technology, I sometimes hanker after the good old days of photography!