One time I was sent on a temporary work assignment with a roofing company, and I had never done any kind of roofing work before then. I was mostly asked to haul materials from site to site. One of the regular roofers needed help making chalklines, and he asked me to hold one end of a string while he stretched it out to a row of shingles. When the string was tight, I was supposed to pull up on it and let it hit the roof. The chalk would create a straight line he could follow later when he started shingling that part of the roof.
I was surprised to see how such a low tech tool like a string line could work better than a high tech laser leveler.