formula_48 is called the reduced scalar electric potential field. formula_146 is called the reduced radius. The existing groups may be recombined to form two other dimensionless groups for substitution into the differential equation. The first is what could be called the square of the reduced inverse screening length, formula_147. The second could be called the reduced central ion charge, formula_148 (with a capital Z). Note that, though formula_149 is already dimensionless, without the substitution given below, the differential equation would still be dimensional.