An unexpected bonus for users of GPS on ocean passages is that many sets will read out a great circle course on request. Some do not even need asking. Just install a waypoint at your destination, make sure the ‘Nav set-up’ is delivering the right goods, punch in ‘Go To’, and the black magic will give you your best great circle course. It even tells you how far you have to go. No more struggling with trigonometry or dog-eared gnomonic charts!