A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2021 Jan 16, 19:03 -0800
A while ago I asked about the calculation of Z. It turned out that there were four basic formula tyes, depending on the inputs - d t l, d h l, d h t or h l t. Your formula is of the d t l form. Checking my notes I have seven references to the d t l formula but only one reference provides a derivation. I have attached a page from Norie which shows the derivation of the A + B = C formula. Maybe from this you can derive your formula?
Do not worry if you cannot. Decades ago when I was at school I considered myself brilliant at trigonometry. Today I get lost if I attempt even the most basic derivation. I am happy to accept formulas as given. I mentioned the four types of formula for Z. I checked each one with a pocket calculator to satisfy myself that they were correct.