Hi, by reading the Einstein's original derivation of the E=mc2 formula (http://www.fourmilab.ch/etexts/einstein/E_mc2/www/), Einstein does an approximation by neglecting higher order derivatives before arriving at E=mc2. But, as far as I know, E equals mc2 precisely. Does anyone know why Einstein didnt derive the equation precisely? I tried to play with the paper a bit to make it spit out the precise equation but didnt have much luck-I must be overlooking something. Could someone help me with this one?