Pulling film you don’t know the development time for
I recently had to pull-develop a roll of APX 400, which I unintentionally had exposed at EI200 or even EI100. And I couldn’t find developing times for XTOL online for pulling APX. But I found an entry in a Flickr group, that suggested using 2/3s of the original developing time per stop pulled. That sounded reasonable. So, for my APX 400 in XTOL 1:1, this meant instead of 12 minutes at 20 ℃, I developed for 8 minutes. The negatives came out looking fine.
(This little accident happened, because I loaded APX 400 via a bulk-rolled canister with a 200 ISO DX code into my Leica Mini, which is an automated camera, where you can’t set the ISO manually. And the DX code was even partially covered by tape that I used to label the film. The tape meant, the camera might not have been able to read the DX code at all, making it fall back to its default ISO setting. Which is probably ISO 100 from what I gathered online. Either way, I ended up with an overexposed roll. The question was if it was one stop or two. I decided it was two. But I only compensated for one stop in development, as I thought it’s probably safer to overdevelop a little bit, rather than ending up with too-thin negatives in case it was actually only one stop overexposed.)