Apple Watch Active Calories vs Move Calories

Does anyone know why move calories and active calories are always so different? My move calories are 1292 and active calories only 505? How are they so different when they both describe calories burnt from being active? Additionally.. My stand hours are incredibly inaccurate. I have not stood for 13 hours today. I did 3 gym classes (2.5 hours worth) but the rest of the day I was sitting studying.. Not standing for 13 hours.. Second guessing the accuracy of these watches.