The following rules are attributed to him: Using the concept of similar triangles he was able to calculate the height of pyramids by comparing the size of their shadows with smaller, similar triangles of known dimensions.Since the average lunar month is 29.5 days, over 12 months this would produce a total of only 354 days as against a solar year of 365.25 days.To keep the calendar aligned to the seasons they added seven extra months in each period of 19 years, equivalent to the way we add an extra day in leap years.Similarly he calculated the distance to ships at sea by noting the azimuth angle of the ship from a baseline of two widely spaced observation points a known distance apart on the shore and scaling up the distance to the ship from the dimensions of a smaller similar triangle.In this way he was able to calculate the distance to far off objects without measuring the distance directly, the basis of modern surveying.

Background We think of a battery today as a source of portable power, but it is no exaggeration to say that the battery is one of the most important inventions in the history of mankind.