NavList:

I said:  To get wind direction you’d have to rotate the disc until the wind vector stood up and down parallel to the centre line, so a certain amount of imagination would still be needed.

Well, as with the Dalton, there always turns out to be an alternative way of doing something.  The picture in the book here http://sliderules...8110158 gives a hint as to how you could find the direction of a vector which isn’t at the centre of the disc without too much imagination.  It relies on the fact that the origin for the drift scale is at the pivot point of the ruler. Wiggle ruler and disc until the ruler lies along the vector.  Note the bearing at the top of the disc (you could use that spare cursor on the edge of the disc to mark it) and the drift indicated by the ruler.  Add a starboard drift scale or subtract a port drift scale ruler indication to get wind direction or its reciprocal.  DaveP