Mariner's Astrolabe, Double Entry Bookkeeping, Luca Pacioli, Leonardo Davinci

Mariner's Astrolabe: It was a tool used by sailors. You had to use two hands to hold it. It read the angles of the horizon. The astrolabe was successful all around the world.

Double Entry Bookkeeping: Double Entry Bookkeeping came to be after the Holy Roman Empire split into three kingdoms. Double entry bookkeeping protects you from theft because most criminals were dumb.

Luca Pacioli: Luca Pacioli went to an abacus school in Italy that taught arithmetic and business skills based on Arabic numerals. He wrote a book about chess. He popularized the double-entry accounting system. He wrote many books.

Leonardo Davinci: Leonardo Davinci was a famous painter and inventer. He is most remembered for the Mona Lisa.