ThispaperpresentsanotherformalproofforthecorrectnessoftheDeadlineDrivenScheduler(DDS).ThisproofisgivenintermsofDurationCalculuswhichprovidesabstractionforrandompreemptionofprocessor.Comparedwithotherapproaches,thisproofreliesonmanyintuitivefacts.Thereforethisproofismoreintuitive,whileitisstillformal.