These numbers might explain why a prior poster has troubles getting good grays from the new MG Deluxe (aka "MG V"): Its contrast is higher than MGIV. And these numbers provide the solution: Use the next softer (lower numbered) filter. BTW, according to Ralph Lambrecht's excellent book "Way Beyond Monochrome" (2nd ed.), pages 298 and 303, the ISO standard for grade 2 is ISO(R) 105, which yields an exposure range of 3.5 stops (on the paper) between zones II and VIII.
Mark Overton