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The machinist level has a precision of 0.0005" per 10", it is an 8" long level, I think that's about 10 seconds of arc per division. I set up on a cast iron table saw table. I clamp a 2" x 22" aluminum carpenters level to the table with a 3/16" drill bit shank under the carpenters level to act as an adjustor. I place the machinist level on top of the carp. level and roll the shim under the carp. level to acheive  "level" on the machinist level.  I then place the square flat section of the Abney level on the carp.level, adjust the protractor until the bubble is centered on the crosshair. I then read the "index" errror, on the protractor scale. It is about 30', 30" was a typo.

With the water level, I screwed one end of the vinyl hose to my porch at eye level, and the other end screwed to a tree 40 feet away. I simply tried my best to hold the Abney next to the miniscus at the porch end and sighted the miniscus at the tree end. Pretty crude.  Got 40' error, which in my mind is in general agreement with the machinist level method given the crudeness of the water level. It's pretty easy to see the red food colored water through the clear tubing. When time permits, I will use the water level at a longer span and darker liquid, grape Kool Aid maybe.

Attached is the data from shots taken today.  Results seem pretty far off from the Anti Spoof numbers. Not sure why. I believe my technique improved as the sights progressed.

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