Uh oh. If you're asking for me to share my math, there must be something wrong with my multiplication (which is very likely).

I finished my exposure and brought my camera and notecard in. I have an aperture scale in one of my photo books that only goes to f/64. I extended that out to f/512, which is the first full stop past my aperture of f/381

I figured out the aperture of my camera by dividing the pinhole diameter by the focal length. My focal length is 7.5 inches, which multiplied by 2.54 to get 19.05 cm. i multiplied that by 10 to get 190.5mm. I divided that by 0.5, which is my pinhole diameter. That gave me an aperture of 381.

I rounded up to f/512 because I knew underexposure was a problem. I didnt adjust for reciprocity the first time because I was like "well, let's see what happens before I start adjusting times." The negative turned out to be more underexposed than I anticipated

My second negative is ready to be developed, so I'll see how that one looks before reporting back here