Scott curls are the best exercise for building biceps I have ever seen. I am going to take the liberty of calling them Scott curls even though I didn't invent the exercise. Over the years however, I have perfected the design of this little bench to where it is as close to perfection as anything I have been able to achieve.
When it's designed correctly it's great. If not, it's lousy. The normal flat faced bench is not very good for biceps work. There are many exercises that will do a better job. But let's assume you have a well designed bench with at least a convex face. The key to this exercise working its charm requires a few specifics.