A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John Pinto
Date: 2021 Jun 3, 13:52 -0700
Let us say we could actually see this Sun in that instance. How would we calculate Z2? That is really the source of the question about the large negative F value. It is a little ambiguous (to me) in the NA explanation for this unusual case.
Pretty straightforward if F is positive how to set Z2 in the form but if F is negative and its absolute value is greater than 90 I'm not sure how to use the Z2 value in the NASR table to fill in the Z2 value in the form.
Do you first negate the Z2 value from the table and then perform 180-Z2 (subtracting a negative is just addition, so it just becomes 180+Z2) or do you first perform 180 - the Z2 value from the table and then make the result negative? You get very different answers for the resulting Z2 in the form dependnig on which operations you perform first.
It is unclear to me if this unusual case was even considered in those instructions.