Six Sigma is a set of techniques and tools for process improvement. It was introduced by engineer Bill Smith while working at Motorola in 1986. Jack Welch made it central to his business strategy at General Electric in 1995. Today, it is used in many industrial sectors.
One acre equals 0.0015625 square miles, 4,840 square yards, 43,560 square feet or about 4,047 square metres (0.405 hectares) (see below). While all modern variants of the acre contain 4,840 square yards, there are alternative definitions of a yard, so the exact size of an acre depends on which yard it is based.
An acre is a unit of area equal to 1/640th of a square mile. It is about the size of an American football field. A square yard is a unit of area equal to a square that is one yard on a side. It is equal to 9 square feet, or about 0.836 square meters.