Wow there is a LOT of information out there on this topic.
B&W film developing
- Step by step tutorial for developing Kodak TMax films
- Kodak PDF on developing their films
- B&H Photo’s very detailed article on film developing
- DIY Rodinol – make your own developer at home
- The Massive Dev Chart – figure out your development times
It’s the same film as 120 film, on a smaller/tighter spool. 620 Film was a Kodak thing, and today is on the market for about twice the price as 120 film. Why? Because you’re paying for someone else to reroll that 120 film onto a spool for you. Here are a couple of do-it-yourself methods. Just make sure to ask for your spools back!