You can use it to explore the operating principle of the gearbox, engage any gear and even use transparency to examine the inner workings.
To view the model you need a VRML viewer: a plug-in for your operating system that allows you to view the Curta, and other VRML worlds.
Installing the recommended browser is free and automatic. I does not expire, but a little logo floats trough the scene. Just ignore it. It helps if you imagine that its a flying saucer with aliens looking at this amazing gearbox too!