A centimetre (American spelling: centimeter, symbol cm) is a unit of length in the metric system, equal to one hunredth 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.