Erlang is regarded as the founder of queuing theory and of operations research. His formulas, designed and published in 1917, enabled early telephone switching systems to become operational. These formulas give the probability that a user will encounter a busy signal instead of a dial tone, or the length of waiting time for a system that can hold calls. They are used to calculate the number of circuits needed to give a specified level of service. Erlang's formulas may be applied to any system with a limited number of servers and customers that arrive at random times.

Agner Krarup Erlang was born on January 1, 1878, at Lonborg, near Tarm in Jutland, the mainland of Denmark. His parents were Hans Nielson Erlang, the parish clerk and schoolmaster, and Magdalene Krarup Erlang. Many of his mother's family were clergymen. Erlang had an older brother, Frederik, and two younger sisters, Marie and Ingeborg...