[quanloh]

In my region at least, -5 ~ -2°C, or -5°C ~ -2°C. If the something is making people confuse, we replace it with a suitable substitution. Re-educating people is really just last resort. Is there anything keeping us from changing it other than ego?

[CRConrad]

In all countries I've lived in (and until right now, I thought the entire world), that would mean "-5 is approximately equal to -2".