Quote Originally Posted by Ian Grant View Post
... sold as Calbe RO9, APH09.

The problem is that the two versions don't behave quite the same. many German and Continental EU photographers prefer the older version which is why people like Mirko ant Fotoimpex sell and distribute both.

I tried them side by side. Same film (APX 100), same light, same object. The density was slightly different but nothing else.

Please keep in mind: Rodinal and sisters don't like overdevlopment and high developing temperture - this lead to grainy results.