I made it a habit to print the pilot log of SD and take this paper copy with me while flying. This as a safety measure for if my iPad fails. This weekend I tested this by using the printed log and my paper chart. I noticed that on some legs there was a difference between the heading on paper and the actual heading needed to reach my waypoint. There are of course several reasons to think of, like wind was stronger as predicted or became stronger/weaker between the moment of printing and flying etc. However it made me also wonder how SD calculates the wind on various altitudes (I was flying at 3000ft.) as the only weather info I see are the Metar and TAF but they do not contain the wind on various altitudes. Afterwards I played around a bit and compared the wind given by SD with the wind predictions on various altitudes and although the do change when changing the altitude it is not always in accordance with the wind predictions. So it would be good to understand how SD is calculating the heading so one can correct in case you need to fallback on old fashioned navigation.

Regards, Tom

SkyDemon knows the forecast wind at all common VFR altitudes at every location on the globe. It performs standard wind drift calculations to work out what heading you need to fly to achieve your desired track across the ground. You can see the wind values by looking at the barbs shown on the map.