postReference_greyWedge

The grey wedge: one column per whole stop from -10 to +10, each middle grey (0.18) at that exposure.

Drawn unlit by @builtin::shaders.referenceChart, so a picture of it is measured against the light its properties state. Part of the post-verification reference scenes (@builtin::scenes.postReference.*); @builtin::modules.postMetrics reads them.