When any one of the following SAS date formats are applied to a numeric subgroup variable in PROC SHEWHART, PROC MACONTROL or PROC CUSUM

MONTH
MMYY MMYYC MMYYD MMYYN MMYYP MMYYS
YYMM YYMMC YYMMD YYMMN YYMMP YYMMS

the control chart will be scaled incorrectly. The problem will be evident in one of two ways: 1) each subgroup value will be repeated several times, or 2) each subgroup value will correctly appear once, but the plotted positions of the subgroup statistics will be shifted slightly to the left or right of where they should be placed.

To circumvent this problem, any SAS date format other than those in the above list should be applied to the subgroup variable.