If you sit in a car for an hour, which I don’t recommend, you’ll take a closer look at things outside your car. For example, the 18-wheeler next to me was from Quebec and had a lot of the aerodynamic, fuel-saving add-ons to the trailer. In the photo above, you can see the under-trailer AirFlow Deflector or Le déflecteur AirFlow. This thing is supposed to deflect air around the wheels instead of having it drag. It will save you up to +/- 7% on fuel. Wait, what?
I can’t figure why they would put +/- except that they couldn’t figure out which was appropriate. If you say “Save -7%” is that a double-negative or emphatic negation? Is this a translation issue? In English, “Save up to 7% on fuel” is clear enough without indicating a sign. If it was possible for the addition of the deflector to add 7% to your fuel costs, this would be a very tricky way of saying so. A brochure from the company now says “up to 8.5%,” so they’ve dropped the sign in current iteration. If you can comment on what the French would be, feel free.