Figure vsg.3 : Period Variation (dp/p) Trends. Changes in grating dp/p with time are shown. The dashed lines represent the dp/p value derived from the 9611 set of VSG retests (not all facets have LR version 3.+ data prior to this retest.) The VSG retests at 9707 and 9801 (as well as initial LR version 3.+ tests if they exist) are then normalized to this period. The dotted lines represent dp/p changes of +/- 30% from the 9611 dp/p value.