Why don't people use slide rules anymore?

Answer 1

The use of slide rules declined quickly after the introduction of inexpensive calculators. By 1976, calculators could be purchased at prices competitive with slide rules, and since their use did not require special training, they were more accurate, and they had greater functionality, it made little sense for most people to get slide rules.

There are still some slide rules being manufactured for special purposes, however. One such is a circular proportional scale used for determining the size to make a copy on a copy machine according to a different size of paper from the original.