I probably don’t need to tell you that measuring diagonals is an excellent, fool proof way of checking something for absolute squareness. There is even an app for it these days… (just search for ‘construction calculator’), just put in the two side lengths and it will calculate the diagonal length for you, but ya still gotta’ physically measure it and that’s where the fun starts…
I don’t know if I actually ‘invented’ this method, but I’ve never seen anyone else do it, so I’m going to claim it until a bigger guy comes along, thumps me and says they invented it… 😉
I started doing this a while ago as I often struggle to get the tape to stay on the edges of whatever it is I’m trying to check, which for me is often timber related. Walking back and forth to re-hang the tape is annoying. And sometimes the situation is that you can’t quite reach the end you want to check, or you have to guestimate the actual measurement because something is in the way and you can’t hold the tape past the end or it’s in an awkward corner etc.
So here’s what I do… move the measuring points. Yup, just move the measuring points inwards a little so you have great access and if you can, mark the points with a little nail. Nails are great as you can hook the tape end over the nail head and pull really tight and it’ll not fall off.
Now there is a caveat, you absolutely must ensure that you are accurate with your new measuring points. In these photos I moved the top side down 100mm or 4″ and the lower points I lifted up 600mm or 24″. this meant I could easily reach the nails from my scaffold and I could easily see the tape measure against the nail head. You also need to ensure that the nails are in the same place in the material. I measured 24mm in from each edge for example (or centre point of the rafter).
So there you go, I hope I’ve explained that properly and it makes sense. It’s a neat little trick which takes a minute to set up, and gives you a really easy way of measuring diagonals. Incidentally, in case you were wondering why I was being so pernickety about These rafters being absolutely spot on for square… It’s because a clear plastic roofing system is going on. The 600mm wide sheets are totally square and need to sit exactly on each rafter with zero ‘wiggle room’ (technical term!).
Stay well and be careful, there is a lot of sharp stuff out there and you’re all soft and squidgy…