Slide rule

 Slide rule:

• Slide rule was invented by an English mathematician named Wialliam Oughtered in 1620SA.D.

• Slide rule has 2 rulers engraved with numbers.

• The purpose of slide rule is for calculations of trigonometry, sum, differences, multiplication, etc.

  
  
  

• The features of slide rule are as follows:

    a) it is the first analog computing device.                                     

        b) it is based on John Napier principle.

        c) A slide rule does not depend on electricity or 

                      batteries.

source:wikipedia.org