A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2017 Aug 31, 11:55 -0700
"Also I wonder why the Chapter 10, Accuracy advises to use the different corrections for the lower and upper limbs of the Sun (the -13.5' and +18.5' respectively). Yes, their sum is the very familiar 32' of the Sun's diameter, but why they are different?"
The limb correction has been summed with refraction which gives different values for upper and lower limb since refraction is always negative. The Nautical Almanac also sums limb and refraction into a single correction.