Casio Waterproof Calculator WM220MSBUThis Casio Water and Dust Prof Mini Desk Calculator is water and dust resistant so you can use it indoors and outdoors. It comes with a variety of basic functionality so you can complete simple sums and equations. The keys are colour coded which makes it easy to distinguish between different functions. This calculator is suitable for basic functions around the home or in the office. It has a large display so that you can easily see your calculations.