The real ISO is in the manufacturers data sheet for Formapan 400, the box speed in marketing hype to a degree.
Originally Posted by marciofs
The Formapan 100 data sheet also seems accurate, not tried Formapan 200 much.
Forma have provided the contrast, fog and ISO dependency for time and temp for three developers.
formapan 400 datasheet
Then you need an adjustment for your developer, meter/shutter and metering technique.
Digital truth is closer to 'Analogue Porkies'
Rodinal @ 20C 1+100 stand will be in the 250-320 range with low contrast, but you may not like the rendering, I set my Weston to 250. Pour in the Rodinal invert a few times and set the kitchen timer for 60 minutes. Id also temper the following solutions to 1C, cause the Forma is not as prehardened as Kodak or Ilford film.
Most of my shooting is high contrast.