Originally Posted by MoreCowbell
The thing that I never had to consider before is that every spirit level out there, from cheap to high end, all have a gap between the edge of the bubble and the lines on the vial. When using it you need to estimate how centered the bubble is.
The Grainger paper catalog publishes level accuracies in minutes of arc and maybe the online catalog does the same. You will need to convert between rise:run and arc angle using the tangent function on your computer.
For large distances I use a garden hose and the water level attachment at each end which probably gives me an accuracy of +/- 1/16" in 100'.
Experienced construction workers can tell you what's achievable using ordinary diligence and what kind of accuracy is not worth pursuing.
As far as your own eyeball accuracy, using small drill bits or bits of tinfoil or copy paper (thickness = 0.004") under one end of your level, have you and others make readings and see how you all do. You already know the error in level because you know the thickness of your shim.
Regarding anal, how bad do you have it? If you do the handwashing thing or tapping on things, that's pretty bad.
I've also heard that things have to be done in multiples of two; the first puts a curse on someone and the second takes it away.
And even Prozac is getting some bad press.