How to draw a perpendicular line

[GeoInMo]

I'm running Professional Version 7.0. How does one draw a perpendicular line to an angled line? The system tells me I must select an angle for the perpendicular line but how does one calculate what that angle is? Why doesn't it just assume 90

[Admin 1]

It is assuming 90 degrees. What it's asking for is an existing line angle that the new line is to be drawn perpendicular to.

You can just click on an existing line, regardless of its angle, and it will proceed to create a new perpendicular line in relation to that existing line's angle.