Diagonal / measurement tools

When we use steel tape to measure the object, it is too hard for us to measure the angular distance of opposite angles of the object. And it is also easy for us to make measurement errors. How can we solve this problem? We design a kind of bidiagonal tapeline to solve it. We do a little change about the head of the general tapeline and make it V-Type. Then it is convenient to measure the angular distance of opposite angles of the object.