''
Machines have long been used to ease repetitive labor. Some machines eased the labor of calculation; watches, orrerys, calculators, difference engines, etc. Gears were the workhorse of this age reaching the zenith during the late 19th century only to decline as they were replaced with transisters for most computation.
...
This is the 3rd generation of Babbage Difference Engine made with LEGO. It is modeled after Babbages Difference Engine #1. The 3rd generation operates five times faster than the 2nd generation.
This machine can evaluate polynomials of the form Ax^2 + Bx + C for x=0, 1, 2, …n with 3 digit results.
...
This machine, modeled after the ancient Greek original, can calulate the date and time of solar and lunar eclipses over a hundred year period.
It is an analog computer with over 100 gears and 7 differential gearboxes. It is accurate to a day or two over it's range.
'' [
source]
Also this project is very interesting, showing how make a working 7-segment display with lego technic [
video]