No calculations, just guesswork. I had J. G. Motamedi’s exposure guidelines in mind when I set up the shot.. Took a spot reading (EV12-13), weather was typically overcast and windy, so I picked 3minutes to avoid camera shake.
Highlights start to show after 5minutes – good!
My second plate popped free from the plate holder – £!$%ing ruined.
My third plate was exposed for 4minutes.
Pack up, then head home to continue development under a bank of five spiral fluorescent bulbs.
Hope this helps.