 He then combines, by addition and subtraction, all the differences of latitude and departure, to get the overall difference of latitude and departure, and converts that back to overall bearing and distance made good.Ramon Llull's suggestive 1295 remarks aside, the earliest known reference to "marteloio" is dated 1390, in the inventory of the estate of the mother of a certain Oberto Foglieto of Genoa, where an entry reads "unum martelogium...item carta una pro navegando".The first clear appearance and explanation is the 1436 atlas of Venetian captain Andrea Bianco.