Robert W. Lang
I work among a group of tool addicts, and I fit right in because I am one too. My tool dependency manifests itself in a couple of ways; I hoard the wrenches for routers, but the real monkey on my back is layout tools. My grandfather was a tool and die maker and one of my earliest memories of him is being shown how a micrometer worked. When I was six, I really didn't care if one of the hairs on my head was thicker than a piece of paper, but as I grew older I came to appreciate good tools as well as the importance of careful and accurate layout. When it comes to drawing circles, there is no substitute for a good set of trammel points.
Compasses work well if you need to draw a small circle, but when the radius is more than a few inches, they become fussy and inaccurate. You have to hold everything just right and hope that nothing slips as you swing the arc. When you set a compass down it takes up a lot of space, and bumping one of the legs can make a compass setting slip. About ten years ago my traditional trammels disappeared, and one of the other lessons my grandfather taught me, frugality kicked in. I saved about twenty bucks and bought a tri-scribe. It was a decision I've never regretted, and between the numerous tools I own for drawing circles, this is my favorite.
The two heads lock securely on a steel rule, or any other thin, flat object. They lock securely and easily, and lay flat on the bench. The pencil can be replaced with a steel point or a knife blade, and when not in use the two heads store in minimal space. It's an easy to use, well-made tool that not many people know about. It has some other functions as well, you can use the pencil holder with the standard head of a combination square. If you need to draw circles, you need to have this tool.