The Most Accurate Level There Is
If you learn a few facts about water levels you'll find them far more advantageous and accurate than even a Builders Level, Transit, Laser Level, or spirit level. Not to mention it is a lot faster to setup and use and with only one person.
Note: There's only one tube. The dashed line illustrates putting the tube in a second location. Water Level Kit 10m
10m (32' 9"). Long flexible hose with graduated sight tubes and vent caps.

The least expensive method of determining the gradient of virtually anything is with the use of water. Water seeks a level automatically.
The only way to set levels round blind corners in one go
10 metre long hose 2 graduated end chambers with stoppers
They might be old fashioned but they can still do things lasers can't