I'm trying to find a way to check my developing time, APX100 in Rodinal 1+25. I'm currently at 8 min / 20C. The thing is, I regulary print on grade 5 to get optimal contrast and I've been wondering if the problem is the development or other (enlarger, etc.). So I read about the method of Bruce Barnbaum in his book. He recommends to expose a zone V on paper (comparing it to a 18% card) and then to expose a zone IX catured on the negative with the same time and see if it is blank or very light grey. Anyway, I want to find a way of exposing zone V without a grey card, and I'd like to ask you if the method I found is correct : it is to find the reference time of the negative and then expose the zone IX capture with that reference time, without using zone V as a reference. Will the reference time give me the correct equivalent of zone IX ? Supposing that the exposure is correct.
I hope you get what I mean.

Thank you in advance,