fixed calculate_R when no production_ratios
fixed calculate_R when no production_ratios

NMGRL/pychron,NMGRL/pychron,USGSDenverPychron/pychron,USGSDenverPychron/pychron,USGSDenverPychron/pychron,NMGRL/pychron,UManPychron/pychron,USGSDenverPychron/pychron,UManPychron/pychron,NMGRL/pychron,UManPychron/pychron,UManPychron/pychron