Phenidone with pyrogallol is superadditive and allow to make true two bath developer. Bath A have low acidic pH and developing start only in bath B. Developer increase speed by 1 stop and produce very sharp images.

RD-201 developer
Bath A
Sodium sulfite 50g
Phenidone 0,2g
Pyrogallol 6g
Sodium metabisulfite 6g
Water 1l

Bath B
Sodium sulfite 30g
Sodium carbonate 15g
Water 1l

Developing time 3min in each bath.

Polypan F50 @64

HP5+ @400