This article is from the Glossary of Technical Analysis Terms.
They can be applied both to price and time, although it is more common to use them on prices. The most common levels used in retracement analysis are 61.8%, 38% and 50%. When a move starts to reverse the 3 price levels are calculated (and drawn using horizontal lines) using a movements low to high. These retracement levels are then interpreted as likely levels where counter moves will stop. It is interesting to note that the Fibonacci ratios were also known to Greek and Egyptian mathematicians.The ratio was known as the Golden Mean and was applied in music and architecture. A Fibonacci spiral is a logarithmic spiral that tracks natural growth patterns.