🚀 go-pugleaf

Some thoughts... 

I agree with most of the comments above: plain-Jane minus signs (or equal signs) with figures that exactly match the width of plus signs and equal signs; en-dashes for ranges of numbers, pages, years, measurements, etc., and for things like destinations of a rail or airline route and date ranges.  

However, I would prefer to use an em-dash rather than a word-spaced en-dash for breaks in thought within a sentence. That said, the problem is that for many fonts, the em dash needs a very slight addition of space to keep it from appearing to touch the adjacent letters. And the em-dash is just too long when working with condensed fonts and some regular fonts. For those cases, I will use an unspaced en-dash (unless it, too, requires a slight addition of space to keep it from visually touching the adjecent letters). The en-space (or em-space) with a full word-space at each end just seems to hang separated from the text. Sometimes I will adjust the width of an en- or em-space in my page layout app to give me a satifactory width to the character for a specific font. 

My opinion. No, I can't cite any rules for them. 

Neil