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Tip to tinker with a water level when you do not have the right equipment (laser) to determine the horizontal between two distant points.

A homemade water level

Fit two syringes at each end of a hose (aquarium type) and fill with water.
Tension the hose.
The graduations give more accuracy to the upgrade, reliable regardless of the length of the pipe.

Video Instruction: How to Establish a Level Grade Line for Landscaping - This Old House