NavList:

I am trying to do Cel Nav using an Abney Level as my sighting instrument. Crude, I know. The level only reads on the vernier to 10 minutes of precision, with estimation to 5 minutes. I know it must have some index error which I am trying to determine by sighting the horizon. The only available sea horizon I have in western New Jersey, is to sight down the Delaware River to a point about 5.5 nm away. So far I think the index error is about 32’ on arc. Height of eye being about 3 feet.  Dip would only be used to determine the index error, not used for sights. I figured dip short as 2.6’. Do you think using this dip short horizon is a good method to calibrate the instrument and derive the index error?  Since I am calibrating, should I add or subtract the dip correction?  Laying the instrument on a precision machinists’ level, I have determined the index error as 28’. Naturally, that assumes the optical line of the level is collimated to the outside body of the instrument. This all just an academic exercise. So far the best fix I have gotten is about 12 nau. miles from my real position.

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