Safety stock is often calculated to accommodate a given service level (SL). The two favourite definitions of service are the percent of good cycles and the fraction of demand satisfied by off-the-shelf inventory. The latter definition requires more effort to use. In Brown’s Method the partial expectation, E(z), is first calculated as a function of the expected lead time demand (μ) and its standard deviation (σ), and the required service level. Once E(z) is found, a table is consulted to determine z. Finally, the safety stock is calculated from the formula, zσ. This article presents a new table, accurate to about 14 decimal places, in which E(z) us the dependent variable rather than the independent variable. With this kind of precision the authors were able to extend Brown’s Table to high values of z, while at the same time providing for virtually any number of significant digits. the article also includes a simpler version of the present computer program (single precision), which yields about four decimal place accuracy. The double precision program actually used is available on request but is somewhat complicated and depends on the computer used (the authors used a TRS-80).
