TIL a chalk line can drift up to 3/8 inch on a 12 foot span

Found this out breaking down a wall in a 1940s house last week. I popped a line to mark a stud layout. Snapped it, then measured my marks. They were off by almost half an inch at the far end. Turns out if the chalk line is stretched unevenly or the reel is tilted, the line arcs slightly. I looked it up on a framing forum that night. Lots of guys said they check with a straightedge after snapping. I've been setting door jambs off my marks for years without checking. Now I'm wondering how many of my past cuts were off because of this. Has anyone else run into this on longer spans?

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