I calculate the slope of a line with the following equation:

(in VB)

slope=(y2-y1)/(x2-x1)


I would like to convert this slope to a bearing (i.e. the angle from the North), it seems that I would get the angle with

Atn(slope)*180/PI

however, it seems it's not the bearing...
and how do handle those slope with negative value?

Thanks very much!!!