A typical GPS readout of a Lat/long position serves up 3 places of decimals. To put this in perspective, 2 places gives accuracy to 20 yards. The third is purporting to pinpoint the span of our outstretched arms, which used to be called a fathom. It’s hard to imagine anything other than the most accurate harbour chart being drawn to anywhere near this degree of precision – never mind any horizontal datum issues. More often than not, then, for the practical purposes of the cruising sailor, the last number is a waste of time.
It’s not long since any navigator would have been thrilled to know where he was to a single decimal place. Two would have been like Christmas so, on most occasions, we need only read the first ‘point’ of a mile. On a passage chart, the pencil line thickness may be that in itself. Wrestling with more decimal places than we need winds up stress and encourages number-crunching errors. There’s a time and place for everything.
