A Thousand Words  wrote:

I remember my father using a slide rule. He was in construction and was studying engineering. It fascinated me to watch him. this was in the late 60's/early 70's.

True.  Plus, the space race began with those engineer's slide rule things and were used on the Apollo missions by the astronauts as the Pickett & Eckels slide rules (1944) were lightweight magnesium and aluminum models and were really expensive too.

I was amazed at the Abacus people too who often beat the calculator guys later on.  Chinese version had two beads on the top level, and the Japanese improved on it with a single bead for the 5's place.  Many could later do math in their heads by visualizing the thing, and some could do long division and multiplication with them too.

Nor-Cal Photography wrote:
What happened to the good, 'ol slide rule????

They were okay for some applications but woefully imprecise in others.  For example, they are okay in estimating the square footage of a room, but I wouldn't trust it to calculate the orbit & trajectory of an attempt to land on Mars.