If you happen to have a good ruler (again, 1720s... Those also cost money or time to make). A ruler and a T-square would work. But still, it's more complicated and requires a lot more bench to secure things in place at angles than folding a piece of string in half.
Well... Yeah. It costs money and/or time to make things. That's as much true now as it was back then, but I don't think a ruler would have been particularly difficult to make, even with 18th century technology.