NavList:

Patrick Twohy, you wrote:
"I plotted a sun shot two ways -- the traditional way via an AP with whole-degree of latitude/whole-degree of LHA, and with an AP at the DR position through your "app." Both yielded an identical LOP, which is excellent. I particularly appreciate that the math is necessarily different with the two methods."

Using the "DR" or any other convenient point near the vessel's likely position as an AP is fundamental and standard in the intercept method. There were paper methods that suggested the DR as the AP long before the whole-degree rules appeared Only the short tabular methods from the late 20th century have those peculiar requirements for the AP coordinates. It is a failure of the celestial navigation education system (non-system!) that navigators end up thinking that whole-degree values for the AP and LHA are essential to the navigation mathematics. They're not. They're essential to the process that is specific to the construction of the short tabular methods.

The math here is not "necessarily different", and it's spelled out in detail (and as I say, it's standard) in the back of every Nautical Almanac published in the past 37 years. There are numerous apps that do exactly the same thing. Rob's app is unique for running on a specific model of TI programmable calculator.

Frank Reed