John Napier was a famous Scottish theologian and mathematician who lived between 1550 and 1617. He spent his entire life seeking knowledge, and working to devise better ways of doing everything from growing crops to performing mathematical calculations. He is best known as the discoverer of logarithms. He was also the inventor of the so-called "Napier's bones". Napier also made common the use of the decimal point in arithmetic and mathematics. http://www.johnnapier.com/

Napier's bones (or Napier's rods) and logarithms: http://www.youtube.com/watch?v=ShjoKnSm9ds

Logarithms were introduced by John Napier in the early 17th century as a means to simplify calculations. They were rapidly adopted by navigators, scientists, engineers, and others to perform computations more easily, using slide rules and logarithm tables. http://en.wikipedia.org/wiki/Logarithm

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece. http://en.wikipedia.org/wiki/Clock

A sextant is an instrument used to measure the angle between any two visible objects. Its primary use is to determine the angle between a celestial object and the horizon which is known as the object's altitude. Making this measurement is known as sighting the object, shooting the object, or taking a sight and it is an essential part of celestial navigation. http://www.mat.uc.pt/~helios/Mestre/Novemb00/H61iflan.htm