It is easier to use and more accurate than using a bubble level and line, or tape measure. It can be done by ONE person, It can be used around corners from your reference point. I have used it to redo my entire perimeter drain system on my house and redo my back concrete patio to ensure slope and proper drainage, as well as level the pier blocks for my patio and shed to ensure they are all level.
It is CHEAP to build! It is SUPER ACCURATE! It is FAST to use!!
I searched the internet and specialty tool shops around my area and found similar but inferior products available for in excess of $100.
Here is a site that not only sells them but offers great explanations on how to use them.
I preferred building my own as it was a lot cheaper, and I had most of the materials already on hand.
This cost me $15 for the tubing and ruler but has saved me thousands in man hours!!!!!
Step 1: Water Reservoir
I used a recycled water container typically found in office water coolers, and installed a 1/4 inch plastic tubing approx 50 feet long through a rubber grommet in the side. This is only a pressure fit, but it was extremely tight so there has never been a leak.
The end of the plastic tubing I attached to a 24 inch long piece of recycled 1/2 inch conduit with a 24 inch ruler attached to it with zap straps. Do not plug the hole end of the tube!!!!! The longer the ruler the more latitude you will have with making measurements outside the zone of your reservoir limits.