I find that sometimes I need to work out the geometry of a project in a hurry and do not have time to draw it out. I use a Gilbert or mecanno erector set to prove the concept or mechanical actions. Both sets use a scale base of .500 in. or 12.7 mm for the spacing of the holes in their parts so it makes it easy to calculate the travels and ratios of the actions. After the project is proven in concept it makes it easier to make the necessary drawings without a lot of wasted time. --richard