The number of parameters refined in the least-squares 
               process. If possible this number should include 
               some contribution from the restrained parameters. 
               The restrained parameters are distinct from the 
               constrained parameters (where one or more parameters 
               is linearly dependent on the refined value of 
               another). Least-squares restraints often depend 
               on geometry or energy considerations and this 
               makes their direct contribution to this number, 
               and to the goodness-of-fit calculation, difficult 
               to assess.