Thomas Fuller, an African sold into slavery in 1724 at the age of 14, was sometimes known as the “Virginia Calculator” for his extraordinary ability to solve complex math problems in his head. He was asked how many seconds there were in a year and a half, he answered in about two minutes, 47,304,000. Again he was asked how many seconds a man has lived who is 70 years, 17 days and 12 hours old, he answered in a minute and a half 2,210,500,800.
One of the men was working out the problems on paper, and informed Fuller that he was wrong, because the answer was much smaller. Fuller hastily replied, "'Top, massa, you forget de leap year." When the leap year was added in, the sums matched.