Height of a Book or a Tower clock

Ask a friend to show you how high the book he is holding would be from the floor, if he stood it up on one edge. Then check his statement. He is sure to guess wrongly: the book will actually be half as tall. Furthermore, better ask him not to bend down to show how high the book would come up to, but provide the answer in so many words, with you assisting a table lamp, say, or a hat. However, it should be one of you having grown accustomed to seeing at the level of your eyes. The reason why people err is that every object diminishes in size when looked at edge ways. We constantly make the same mistake when we try to estimate the size of objects that are way above our heads, especially tower clocks. Even though we know that these clocks are very large, our estimates of their size are much less than the actual size. Ordinary human beings look like midgets next to it. Still it fit is the orifice in the clock tower shown in the distance, unbelievably. Estimate the size of the dial of famous Westminster tower clock when brought down to the road below.