Hmm, interesting solution. I think that sentence in the lesson book needs to be rewritten. "regardless of its meaning" is referring to whether it means feet, or minutes of arc, or a derivation of a similar item such as A and A'. The statement should read "regardless of its *mathematical meaning".
The new Nemeth punctuation list include the UEB single quotation marks. The opening (left) single quotation mark is (6, 236) as it always has been. The closing (right) single quotation mark is (6, 356). In your example, if you are certain these are punctuation marks, you should use those symbols.