A centimetre (American spelling: centimeter, symbol cm) is a unit of length in the metric system, equal to one hundredth of a metre, which is the current SI base unit of length. Centi is the SI prefix for a factor of 10 ^{− 2}.^] Hence a centimetre can be written as 10×10 ^{− 3} m (engineering notation) or 1 E-2 m (scientific E notation) — meaning 10 × 1 mm or 1 m / 100 respectively. The centimetre is the base unit of length in the now deprecated centimetre-gram-second system of units.

Though for many physical quantities, SI prefixes for factors of 10³ - like milli and kilo - are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements. A centimetre is approximately the width of the fingernail of an adult person.

What is a Furlong?

A furlong is a measure of distance in imperial units and U.S. customary units. It is equal to one-eighth of a mile or 660 feet or 201.168 metres.

Five furlongs are approximately 1 kilometre (1.00584 km to be exact). Since the original definition of the metre was one-quarter of one ten-millionth of the circumference of the Earth (along the great circle coincident with the meridian of Longitude passing through Paris), the circumference of the Earth is about 40,000 km or about 200,000 furlongs.