Good morning- afternoon. First of all, apologize for my bad English. After reading about how the expected value of an operator <q> is what we would measure in classical mechanics and that for the case in which we have various of them it is not trivial to deduce in which order these operators go for the lack of commutative propriety. <px> is not <xp> and that the true form to measure <xp>=(1/2)< xp+px>. I haven’t found how to calculate )< xp+px> If anyone could point me a webpage or book where that is explained, it would be a great hel for me. Thanks.