Be it known that this writer was never a math wizard. He made the mistake during his schooling years of concentrating on English and literature instead of math or physics. And once he got into the machine shop he discovered that various forms of math were more useful for making a bit of the long green than parsing sentences or explicating A Farewell to Arms.
     During the days of your faithful correspondent's apprenticeship the slide rule was the main instrument for the calculation of multiplication, division and percentage. It was quick and accurate. Then the electronic calculator came to for and that all passed and the result was that more time was spent punching digits into a Hewlett-Packard than was spent sliding a K&E or or Pickett. And it finally descended to the point where the mechanics and machinist would use an electronic calculator instead of doing the calculations on paper.
     It was then that this writer knew that the end of the world was coming. In less than ten years an instrument that had sent man to the moon was replaced by an instrument that results in more than ten years to build and fly a fighter jet.
     Here are a couple of appreciations of the slide rule:
      Joe Moran's blog: Slide rules rule OK
     Why a slide rule is better than a computer