What it does: It's your go-to solution for making sure you get your measurements and angles right when you're drawing a pattern, grading (going up or down a size), taking clothes in or just trying to make a perfect shape for attaching or customising.
Price: About £24
Where can you get one?: Morplan
Worth it because: It's the smarter, slicker sister of the graded setsquare. You've got all your parallel lines and right angles, plus it covers curves.
Okay, break it down for me: Alright, then...