The first and best instruments are the traveler’s own eyes

“[Percy] Fawcett was taught not just how to survey but how to see — to record and classify everything around him, in what the Greeks called an autopsis. There were two principal manuals to help him. One was Art of Travel, written by Francis Galton for a general audience. The other was Hints to Travellers, which had been edited by Galton and served as the Society’s unofficial bible. The 1893 edition stated, “It is a loss, both to himself and others, when a traveller does not observe.” The manual continued, “Remember that the first and best instruments are the traveller’s own eyes. Use them constantly, and record your observations on the spot, keeping for the purpose a notebook with numbered pages and a map… Put down, as they occur, all important objects; streams, their volume, colour; mountain ranges, their character and apparent structure and glaciation, the colour and forms of the landscape, prevalent winds, climate. …In short, describe to yourself at the time all you see.”"

–David Grann, The Lost City of Z: A Tale of Deadly Obsession in the Amazon (2009)