Howdy,
On Mon, 22 Aug 2005, Randall wrote:
>> I'm wondering how this works on sloping ground. Like, if you're doing a
>> pole barn and the ground slopes 8" down over 24'. Seems like if you fix
>> an end to a high side pole then walk around with the other end, when you
>> are marking poles also on the high side the water will be higher than if
>> you're marking poles on the low side.
>>
>> Obviously the water will be level between two points, but wouldn't there
>> need to be a correction made if you're doing it all between multiple
>> points, since the bulk of the water in the tube may be higher or lower,
>> depending on where most of the tube is on the slope?
>
> Nope. Regardless of the location of the intervening tube, the end points
> will be level to a high degree of accuracy. Errors due to local gravitation
> gradients (including tides) will be microscopic. And most people define
> "level" to be equal gravitational potential anyway. Otherwise you wind up
> with water that runs uphill and so on.
I know the two end points will be level. What I wonder about is if the
two end points will be at the same place they were on a previous
measurement.
I.e....
You've got a water level, with all its tubing, on a table. The two ends
are held up against a wall and you mark where the water is.
Next you take all the tubing on the table and drop it on the floor. The
water level just got lower (on both ends), right?
So how do you account for that effect when you're marking multiple posts
(on a grade) from one reference point?
Mark
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