The use of slide rules continued to grow through the 1950s and 1960s even as digital computing devices were gradually introduced ; but around 1974 the electronic scientific calculator made the slide rule largely obsolete and most suppliers exited the business . The use of slide rules continued to grow through the 1950s and 1960s even as digital computing devices were being gradually introduced ; but around 1974 the electronic scientific calculator made it largely obsolete and most suppliers left the business .