That being said, asking someone to calculate control limits by hand in today's world of computer software seems a bit bizarre.
I have two references materials - the handbook and the CSSGB primer. Neither of them list out a d2 table for my reference.
And a 64% pass rate for a certification exam is not unusual. They aren't intended to certify people who are new to the material, but instead those who have several years of experience (ergo the experience & education requirements to take the exam). This means test takers would ideally already be well versed in much of the BOK.
I'm tagging a couple people who might have some insights, although not necessarily on the Green Belt -
Jessica Vallecillo, Amanda Foster - could you let Lisa know how the question banks compare to the actual exam.