"A chessboard and a set of counters makes a formidable calculation device. This is from the final part of John Napier's treatise called Rabdologia, or Rabdology. He called it 'Location Arithmetic as Performed on a Chessboard'. This method of using counters on a chessboard is based on binary and basic algebraic properties, and with only sliding counters on a chessboard we can perform multiplication, division, and square roots, even square roots of irrationals. #maths#mathtricks#mathematics"