Originally Posted by Brewmex41
I got brewers friend on my android. When I changed the field for temperature from 68* to 38* (F) it cut the amount of sugar needed in half.
Could someone explain this to me?
The short answer, as already explained, is "it doesn't".
I hate those priming calculators! The temperature is almost always unimportant, as even with lagers they often have a diacetyl rest in the 60s, and are very confusing to people who try to use them. Also, they have you prime "to style". That's all well and good, if you're accustomed to that, but most people in the US who buy bottled commercial beer do not drink them "to style" and expect about 2.4-2.7 volumes of carbonation in all bottled beer.
The calculator would have you make your English brown carbed to something like 1.5 volumes (totally flat) and your wits to 4.5 volumes (bottle bombs).
Just like with every set of instructions, always ask yourself if something makes sense. If it doesn't it probably is wrong.