To draw a perpendicular line at any point on a straight line is easy when you know how and all you will need is a piece of paper, a pencil, a pair of compasses and a ruler.
Here is how it is done in 5 easy steps...
Draw a line to the length you need and mark on it where you want your perpendicular line to be.
Set you compass so it is open at about 1 to 2 cm wide (now need to be incredibly accurate at this stage) and use your compass to make a semi circle like this on the straight line...
I have marked one point A and the other B to make it easier to understand the next stages.
Open your compass so that it is a little wider, 3 to 4cm wide.
Putting your compass on the point I've marked A, make a mark with the compass. Do the same again but at point B. Look at the above photo to see what I mean.
Where the two curved lines that you made in STEP FOUR meet, draw a line from that point through to the first point you marked off in STEP ONE, Like this...
YOU'RE DONE, IT'S THAT SIMPLE!!!!