That's part of it, but the assumption is that the record is perfect (yet only to one minute) so cardinal equivalency will be calculated from that record. Then the double proration point doesn't need to be calculated using astronomic north until the last bearing-bearing calculation, which is normally two short lines intersecting near the "midpoints".
Ok - thanks all. Got this figured out.
FYI - couple of things of interest.
1. The LaPlace correction for my location is 1.57" - insignificant. But, hey, slop plus overkill equals precision (or is that accuracy?). So, I'm good.
2. Collegue made this observation: how close did the original crews adjust to astronomic? Because those guys ALWAYS followed Tiffin's instructions to the letter. They would often make an astronomic observation, note the deviation from magnetic, then apply a correction to magnetic until the next astronomic determination. How often was that?
@john-hamilton Are you able to send me the file?
