See http://scratch.mit.edu/discuss/topic/30265/ Shows how to calculate the direction of a point from another. The angle it gives goes from -180 to +180 degrees, and follows Scratch's 'point in direction' convention. Also shows the distance between the points, for completeness. Drag the dots to change the direction of the red line.
* updated displays to show only 3dp again (now that Scratch has switched to showing 6dp by default...) The method it uses is based upon the inverse tangent (atan) of the gradient of the line joining the two points. The inverse tangent only returns an angle from -90 to +90, so it needs a bit of extra work to check for the remaining sections (+90 to +180 and -90 to -180).
