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Index error vs. index correction
From: Paul Hirose
Date: 2020 Mar 13, 14:38 -0700
From: Paul Hirose
Date: 2020 Mar 13, 14:38 -0700
On 2020-03-10 12:32, Tony Oz wrote: > I think there should be only one term: either IE or IC, it depends on how you define it. That value - whatever you call it - is just the difference between the true value and the one displayed by an instrument. > Hence the formula: TRUTH - APPARENT = INSTRUMENT ERROR; from which clearly follows if we want to know the TRUTH we must do APPARENT + INSTRUMENT ERROR. On the other hand... On 2020-03-11 14:46, Antoine Couëtte wrote: > From a recording you either : > - Remove (i.e. "subtract") an error, or > - Perform (i.e. "add") a correction. I agree with Antoine. In my view, the error of an observation is the observed value, minus the true value. The correction has the same magnitude but opposite sign. To recover the true value, you either add the correction or subtract the error. Bowditch (1984) is surprisingly elusive on the "sense" of error and correction. However, the master table of sextant corrections says refraction and dip corrections are always negative, which implies corrections should be added. But the Nautical Almanac agrees with Tony. To calculate apparent altitude: H = Hs + I - D where I is index error and D is dip. (See page 280 in the 2020 edition.) Index error, index correction... is there any consensus? Are the definitions whatever you want them to be?
