Here is a handy tip. If ever you need to find a right angle, yet haven't got a right angle tool to hand you can use a simple mathematics trick (yes, your mathematics teacher really did teach you something you can use in real life).
What you need to do is to cut three pieces of wood, it doesn't matter which unit you use but the lengths must be 3 units, 4 units, and 5 units.
Attach the 3 and 4 lengths together at a right angle, and then finally conntect the 5 length piece to complete a triangle. Once the 5 length is connected you will find that the angle where the 3 / 4 lengths attach are a perfect right angle.
Well done Pythagoras!