arranges the Shewhart chart in two levels (rather than the default of one level) so that twice as much data can be displayed on a page or screen The second level is a continuation of the first level, and this arrangement is continued on subsequent pages until all the subgroups are displayed You use the NPANELPOS= option to control the number of subgroup positions in each level If you specify the BILEVEL option in a chart statement that produces primary and secondary charts, you must also specify the SEPARATE option