Mathematically, we can state the law of charge conservation as a continuity equation : d Q d t = Q ˙ ˙ I N ( t ) − − Q ˙ ˙ O U T ( t ) . where d Q / d t is the electric charge accumulation rate in a specific volume at time t, Q ˙ ˙ I N is the amount of charge flowing into the volume and Q ˙ ˙ O U T is the amount of charge flowing out of the volume; both amounts are regarded as generic functions of time.