Original: 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 exited the business.
Simplified: 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.