A NOT NEW METHOD BUT FULLY EXPLAINED !!!

The first problem met by a young beginner during the construction of his first control line model is always the ribs. How to respect the shape and the dimensions of all the ribs ? His (or her) dexterity is not enough good at this stage to product a lot of similar parts. So we use an old and improved method we learnt 30 years ago and which is always the best I know. The block.