I am a unit of measurement. I am rather confused however, because I am used to measure different things. Physicists use me to measure temperature. In that case, I come in 3 different types, named after a German, A British lord, and a Swedish astronomer. In America, they prefer one type, but in Europe they like another. Scientists don't particularly like either of these. In Geography, I am divided into minutes, but I am not used to measure time. And just for good measure, I am not used at all by mathematicians who like to use Calculus. What am I?