Period, mass, and length are dimensionally independent, but acceleration can be expressed in terms of time and length, which means the four variables taken together are not dimensionally independent. Thus we need only p = n − − k = 4 − − 3 = 1 dimensionless parameter, denoted by π π , and the model can be re-expressed as F ( π π ) = 0 , where π π is given by π π = T a 1 M a 2 L a 3 g a 4 for some values of a 1 , a 2 , a 3 , a 4 .