Just a suggestion: You might use = instead of hyphens in front of your numerals bc hyphens can appear to be minus signs. As in . . .
= 21 or + 21 F.
instead of . . .
- 21
In Montana here, we read minus signs quite often during winter.
Sorry for the confusion, Montana.
We do not get to practice using minus signs very often in the Pacific northwest.
The record all time low in Seattle was 0 degrees F, in January 1950.