Dip depends on how high your eye is above sea level. It applies to sights taken with a Kamal or cross staff but not a quadrant or shadow astrolabe. The equation for dip in normal atmospheric conditions is:
Dip = 0.97 x the square root of the height of eye in feet If you do not have a calculator then you can round 0.97 up to 1.0.
If you reckon that your eye is 10 feet above sea level then it is:
Dip = 0.97 x Square Root of 10 = 0.97 x 3.2 = 3.1'.
Dip is always (well, nearly always) negative and subtracted from your reading.
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