1, 24, 51, 10

This clay tablet from 1800-1600 BC shows that ancient Babylonians were able to approximate the square root of two with 99.9999% precision. These are numbers, written in Babylonian cuneiform numerals. They read as 1, 24, 51, and 10.

$$ \sqrt{2} \approx \frac{1}{60^0}+\frac{24}{60^1}+\frac{51}{60^2}+\frac{10}{60^3} = 1.41421296296 $$

The margin of error here is less than \(6 \times 10^7\)