Do you know what a difference engine is? Me neither.
So what is a difference engine? Here is what Wikipedia has to say:
A difference engine is a historical, mechanical special-purpose computer designed to tabulate polynominal functions.
Since logarithmic and trigonometric functions can be approximated by polynomials, such a machine is more general than it appears at first.
Did you understand that completely? Me neither.
However, to make one using Lego bicks and parts impresses me!