address issue #992. ideogram min = min-2*sigma, max = max+2*sigma
address issue #992. ideogram min = min-2*sigma, max = max+2*sigma

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