I'm sorry. I checked one more thing and found an answer. 🙂 In the preliminary section of the 4-4-2023 AN INTRODUCTION TO
BRAILLE MATHEMATICS USING UEB WITH NEMETH, I found this:
The braille symbol for the prime sign is used wherever the print symbol appears in mathematical context regardless of its meaning. When more than one prime sign is used in print, the equivalent number of signs are used in braille. Prime signs must be unspaced from each other and from the quantity to which they apply. In the following example, the prime sign is used to denote feet and inches.
I'll use a prime sign.
Thanks again, Carmen