A blocking board is a great tool if you are crocheting granny squares that you want to get a nice and even result. The board ensures that all your squares are the same size and shape, making assembly easier. 

The plate is made of wood and has a MYO engraving in the center. Note that you will need to get a bunch of nails or similar to tighten the corners. The plate has markings for centimeters (see picture). 

Before you start blocking, carefully wet your squares (too wet squares can damage the wood). Once you have blocked in the desired shape/size, allow them to dry thoroughly before sewing or crocheting them together. Avoid placing your blocking board in direct heat as this can damage the wood.