Kwik Fit, Physics Shit

I'm aware I've been swearing a bit more regularly in recent entries on here, but for the sake of a rhyme, I feel the use of the S-word in the title of this post is justified. Anyway, my point. Read this:

Let Kwik Fit recharge your Air Con while-u-wait for only £44.95. We will replace and recharge lubricant and refrigerant levels in line with your manufacturer’s recommendation. If we cannot improve the coolest vent temperature from your car by more than 10% - then you pay nothing at all.

Let me tell you something about temperature - the scale you are used to is very misleading. If you are of roughly my age, which you quite probably are, then your scale of choice starts at the freezing temperature of water and hits 100 as water boils. The rest of you use a ridiculous system in which various points are defined by weird mixtures of ice, salt, ammonium chloride and the armpit of the scale's inventor (seriously).
In any case, unless you're a pedant with a physics degree, you probably don't prefer the Kelvin scale, at which zero is defined as the coldest anything could ever theoretically be. The nice thing about this scale is that you can say that 20 degrees is twice as hot as 10 degrees, because your zero point actually represents zero thermal energy. Since this is a logical scale for discussing temperature, let's use it to examine Kwik Fit's claim that they can reduce the temperature of a car's air conditioning by 10%.
Let's imagine your car's air conditioning system has been neglected and is pumping out air at 10 degrees centigrade. You take it into Kwik Fit and ask if they can sort this out. Yes, they say, they're pretty sure they can reduce this temperature by 10%. At this point, you pull out a calculator and convert 10 degrees centigrade into the far more sensible 283.15 kelvin, then divide this by 10. You cheerfully point out that you are excited at the prospect of a 10% reduction in the temperature of your car's air con, since the ability to blast air at minus 18.315 degrees centigrade will be something of a novelty. The mechanic tells you to fuck off and get a life, but at least you know you're right.

And now some added bonus features for this post.

• You may have spotted that I used the word 'kelvin' twice in this post (before this sentence, obviously), once with a capital 'K' and once without. This is one of those silly little points that I really want someone to pull me up on so I can go 'aha', and explain that actually you spell units in lower case, even if they are named after a person. Oh, but just so we're clear, if you say "10 degrees Fahrenheit", that's correct because the "degrees" bit is the unit (I think).
  
• A thought: isn't it weird that the Fahrenheit scale was named after a person? My D-grade AS-level German knowledge tells me that the word means "going-ness", which seems a pretty apt description of temperature, the measurement of how much the molecules are bouncing around. It's like if the motion of the planets had been described by Sir Isaac Droppingness.