Human Irrationality 2 – Lefty-Loosey, Righty-Tighty

                This post is about a saying that I play along with when it’s said, but deep down always wished didn’t exist. I’m referring to the mnemonic device “Lefty-Loosey, Righty-Tighty.” For those unaware, it is a trick to remember which way to twist something like a screw or valve in order to loosen or tighten it. However, I can tell you for sure that simply moving a screw right will not make it tighten.

                Okay, so now you’re saying that to tighten it, you need to “turn it right” rather than move it right. The problem here is that left and right are linear directions, not rotational. This is a problem because if you turn something such that one point goes right, there will also be a point that goes left. Let’s look at two valve handles, one that’s turned clockwise and on that’s turned counterclockwise.

                If we assume that we can define a rotational direction by the direction one point moves, then the left one could be any of the directions of the red arrows: right, left, up, or down. Similarly, the right one could be described as: right, left, up, or down. But somehow “left” and “right” are each supposed to refer to one but not the other.

                The explanation I’ve been given is that right or left refers to the direction of the top part of the piece you’re turning. That’s great, until you realize that you won’t necessarily be looking down on the thing you’re turning. Imagine a pipe at waist level, with a valve whose handle is pointing down, so the knob is below the pipe. To tighten this, you need to spin it such that the “top” point of the knob goes left, because you are viewing it from the opposite side.

                The best way to remember is by the right hand rule: if you take your right hand in a thumb’s up position and orient it such that your fingers wrap in the direction you’re spinning, the piece will move in the direction that your thumb points. Then all you need to remember is that to loosen a valve, you want to back it out and to tighten you want to drive it in.

                Finally, I hope this post will make it back to our friends at Microsoft, so they can address this bug I found in Paint while making the above image: