This device is really going back to basics, but to be honest sometimes the most simple of devices are best and cheapest.
In basic form all you need is one length of clear pipe and water. Gravity does all the rest.
The principle and physics of a water level is that water will find its own level wherever it is placed. Tip water onto an uneven floor and it will always find the low spots for you.
Fancy models of water level will have a length of pipe with glass or plastic calibrated reservoirs at each end of the pipe. Unlike laser levels and more critical measuring devices, the water level can go around corners.
You can even add some food coloring to the water to make it easier to see when marking required levels.
When you have filled your length of pipe, hold both ends up together and the fluid within the tube should both be at equal levels next to each other. If not there could be a blockage in the pipe or you might even be standing on a section of the pipe.
Before you start marking, the fluid in the pipe will not be flat, it will be concave as in the image to the left. You should agree with the other person you are marking with, whether you are marking at the low point of the concave or the high point.
Firstly, you need to make sure the length of pipe you are using is long enough to reach all the locations you want to mark. Once the fluid is level you are ready to start marking out.
This is really a two man job as you will need some one at each end of the pipe to confirm to each other when levels have been achieved.
Hold one end of the pipe at the point you know is correct, then lay your pipe on the floor with your finger over the end of the pipe to stop spillage.
Take the other end of the pipe to the points where you need to mark correct heights, hold in a "near enough" position and release your finger from the end of the pipe the fluid will then move up and down in the tube till it settles.
Once it is settled you have achieved a level point between both ends of the pipe, you can then move the pipe up until the fluid meets the height required. The other end of the pipe will be at the same height. You can then mark your wall.
This procedure can be repeated all around the room or building site, giving you multiple points at the same level. You can join these points with a crisp straight line using a chalk line.
As always at DIY Doctor we recommend the use of protective gloves, masks and eye protection when working with dust and debris.