Fix a rounding bug on up.
Fix a rounding bug on up.

mbostock/stack,ImFreeApp/resource-stack,mbostock/stack,Archie22is/stack,Archie22is/stack,ee08b397/stack,bondah/GIS_Intro,ee08b397/stack,banj/stack,gideonite/WIP,fbukevin/weic_d3js,ImFreeApp/resource-stack,bondah/GIS_Intro,atogle/presentations,SoxFace/stack,SoxFace/stack,fbukevin/weic_d3js,tailhook/leap_presentation,banj/stack