(1) A value believed to be close to the correct value of a quantity. The terms first approximation, second approximation, etc. , are used for sequentially calculated values that are successively closer to the correct value.

(2) The process of obtaining a value believed to be close to the correct value of a quantity. Two different processes are recognized: direct approximation, in which an approximation is calculated only once and to a closeness that is considered satisfactory; and (b) successive approximation, in which values successively closer to the correct value are calculated in sequence, the approximation calculated in one step being used as a given value in the next step. The process is repeated until either a satisfactory value is obtained or no change of value occurs or the process begins to diverge or oscillate. This process is also known as an iterative process. Direct approximation provides an answer faster but the formula used are generally more complicated. Successive approximation takes longer to provide the final answer but uses much simpler formula.