 Bench Plane sharpening the ruler trick a three-minute overview. Hola woodworkers, let's talk about the David Charles Worth ruler trick. I'm sure David doesn't feel he invented it, but he's certainly been the promoter of it and it's been adopted by a lot of people that I respect a lot. So you're trying to get your Bench Plane ready blade and you're working on flattening the area you need to flatten on the back. To do that you're putting a ruler on the edge of your polishing stone. You're laying your blade down on that polishing stone and on the back on that ruler. What you've done obviously is you've raised the back of the blade by whatever the depth of this ruler is, which is 0.5 millimeters. This is about 50 millimeters from somewhere in here to here and then this is 0.5. So why does that work? Well first of all, why would we need to flatten the entire surface going back two or three inches on the blade when all we're going to end up doing later anyway is putting our chip breaker on there and depending on how fine of a shavings we're trying to do we're going to go right up to that edge. So everything underneath that chip breaker whether it's flat or not is kind of academic. What's really important is that edge that we have showing because that's what's going to be down there. So how much of an angle are we creating? Because everybody says, hey keep it flat, keep it flat, keep it flat. Well yeah, you are creating a little angle. I've got a ratio of 0.5 height over 50 in length or 1 over 100 if I double both of those. So that's a 0.01. There's a trigonometric function called the tangent. The tangent of an angle is equal to the ratio of the opposite over the adjacent. Well that's what I have here, 0.01. And so if I try the tangent of 0.6 I get an answer of about 0.01. So my conclusion is that I'm putting an angle of about 2 thirds of 1% on that bottom of that plane. So I hope that helps. Probably confuse the hell out of you. Small workshop guy signing off.