There has been a request for an explanation of the water level concept. Cool... a way to waste some time on Saturday afternoon. (It's raining anyway......)
Right. Here it is, set up in the backyard in demo mode..... notice that I have added green food coloring to the water, making it look like the Kool-aid that Tim used to soak bread in (his after school snack). This makes the water easier to see. The level is comprised of two "sticks", 75' of tubing, Kool-aid, electric wiring staples and a base stake.
The base stake is set somewhere close to grade, driven into the ground so it is secure. The stick on the left is left clamped to the base stake during use. The right stick will be freed of the clamp and moved aroung for measuring purposes. Between uses the right stick will be returned to the base and clamped in place, thus preventing tip-over and loss of Kool-aid.....
Okey-dokey, then. Ignore the tape rule, it is for illustration only. The electric wire clamps are installed just far enough to hold the tubing in place from slipping position on it's own, but just loose enough to allow the user to slide the tubing up or down to calibrate the level. In this case I have moved the tube to get the water to be level with the zero mark. Well, close to the zero...
I believe the question was "is it something like john sez...water seeks its own level or some such nonsense?" Yes and No.... Yes, it has to do with water seeking it's own level, and No, it is not nonsense. We take for granted some amazing laws of physics. You have, no doubt, noticed that there are no hills or humps or valleys on the surface of Green bay, disregarding waves of course. On a still day the water will be flat (actually, it will have the same curvature as the surface of the earth, but we'll disregard that).
When you fill your sleever with Guinness does it have any highs or lows in the glass? Of course not, the surface is flat and level.
Does the glass tube on the side of your coffee pot ever read 3/4 of a pot remaining when only 1/8 of a pot remains? Not a chance.
Notice that the surface of the water on the shallow end of the pool is level with the surface of the water at the deep end of the pool.....
If you had two pools next to each other and they were connected near the bottom with a culvert, as you filled one pool the water would run through the culvert into the other as well. How could it not? So, as you fill the pool and the culvert is under the surface of the water, the water continues to flow through the culvert with the surfaces in both pools remaining level. Ah, yes, this is exactly what is going on with a water level!!!
Back to the business at hand. Here you will notice that the inch marks on the level are really only 1/2" apart. Compare the scale on the right stick with the tape rule on the right. This condition will be illustrated below. Also note that the numbers are negative above the zero mark and positive below the zero mark. Also illustrated below.
Anyway, here we are, ready to do some measuring. We are going to raise the right stick one inch, simulating measuring the grade slope.... first notice that the 10" mark on the tape rule is aligned with the right stick zero and the left stick reference line.
After raising the right stick, notice that the 11" mark on the tape rule is now aligned with the reference line on the left stick. This verifies a 1" raising of the right stick. Notice that the water has moved up in both hoses, but only by 1/2" in each!! Also notice that it is now level with the +1" mark on the right stick even though the level of the water has dropped in the hose.
In real life, I would take the right stick to the desired grade or object that is at the right height. It could be the ground, the bottom of the plywood on a wall, the top of a form board, etc. The bottom of the right stick is placed on said object and the hose adjusted up or down until the water is level with the zero mark. Now any up or down motion of the right stick can be read directly in inches plus or minus relative to the reference object. The really nice thing about this method is that it can be done by one person in most cases, where a transit or optical level requires two people. Some of the new laser levels can be used by one person with a grade rod, but setting to zero is not so easy and you need to do the math at each reading.
Good grief, I couldn't leave well enough alone! I just googled "water level" and this is what I found. It's an interesting read about the theory of it all.
If you're still interested, you can check here to see more... Or here????
That'll teach you to ask questions......