George, the guy we hired to do most of our apartment remodel, never ceased to amaze me. He was very talented, detail oriented and quite the problem solver. George spent several weeks going from room to room transforming our apartment. All for less than US$60/day.
When he painted the accent color wall in our living room he needed to make a straight, level line along the bottom of the rounded cove connecting the wall and the ceiling. Not owning a level he showed up one morning with a 14 foot length of clear 1/2 inch flexible tubing. Working with his son, they filled the tubing with water leaving about 2 inches empty. Holding both ends together George lifted the tubing and lined up the water level in each end. He marked both ends of the tubing at the aligned water level.
George took one end of the tubing up a ladder to one end of the wall and his son took the other end to the opposite wall. They held up the tubing ends and lifted them to the base of the cove where they both carefully aligned the water inside the tubing with the line marked on the outside of the tubing, then marked the wall.
Then they took a curtain rod from another wall and used it to connect the two marks. Poof! Straight level line!