This text is missing some spaces, please add them: Guolookedattheaccumulateddifference,namelythedifferenceindegreesmovedbythesuninadaycomparedwiththeexpecteddegreesmovedifthemotionwasconstant.
Guo looked at the accumulated difference, namely the difference in degrees moved by the sun in a day compared with the expected degrees moved if the motion was constant.