A point of reference is a constituent part that determines the size of a model. We use it to calculate how much smaller (or larger) than the original object the model has to Besi-cally, we need some part in our model whose size can be compared with the size of its real counterpart. For wheeled vehicles, comparing wheels-or, more specifically, the diameter of tires-work best Because LEGO wheels have a fixed size, we can easily scale the rest of our model to be the appropriate size.