trial position. See also Bowditch's American Practical Navigator References External links Nautical Almanac, Board of Longitude Collection (Cambridge University Library) Her Majesty's Nautical Almanac Office Online Nautical Almanac The free online Nautical Almanac in PDF format A free Nautical Almanac in PDF format Navigation Spreadsheets: Almanac data History of the Nautical Almanac Sailing books Maritime books