If I do a relatively long East/West leg (yesterday was Biggin to Exeter, for example) if find that the line on SD is significantly displaced from that on the plumbed in GPSs (530/430/Pilot IIIc) to the extent that there is probably over a mile between them at the mid point. Thus, one can have a significant fly right on one and fly left on the other.

SkyDemon uses rhumb lines for planning and navigation. The track and heading shown in the PLOG is a rhumb line, because there isn't a decent way of representing a GC in the PLOG as by its nature, flying a GC requires periodic updating of the heading you're flying.

A long time ago we actually used to have a tool which helped you plot a series of rhumb lines tracking along a GC, but nobody used it so it eventually got removed when the parent feature was being updated.

Tim, I quite understand your reasoning. But you could show the course to steer at the current location. That course would update as you fly along, naturally. But at any point in time, when you view the PLOG, you'd see the appropriate course at this time.

-- Chris.