@pinhole_dreamer: Go to http://www.mrpinhole.com/calcpinh.php and click on "pinhole exposure guide"... of course, you still need to calculate recoprocity for your particular film. If you get a good exposure with guesstimating, I see no reason for complicated calculations, though. I usually just note the Sunny 16 exposure time from the pinhole calculator and guess from there: A little cloudy is 1 stop more, shadow is 2 stops, dark clouds is 3 stops, and so on. When the exposure is several seconds to minutes, a second more or less doesn't really matter anyway.
I've never figured out the "Sunny 16" rule...and I'm horrible at math. I just guesstimate. If it's really sunny, 1-2 seconds with the one one thousand method...and if it's kinda cloudy, 3-4 seconds. Really cloudy? 5-8 seconds. If it's SERIOUSLY cloudy, I don't bother.
I love the smell of fixer in the morning...It smells like...PHOTOGRAPHY!
The photo blog has moved... I Love Film : by Susan McNutt, the mad photographer