Multicenter evaluation of a chromogenic substrate method for photometric determination of prothrombin time. - Dati, F; Barthels, M; Conard, J; Fluckiger, J; Girolami, A; Hanseler, E; Huber, J; Keller, F; Kolde, HJ; Muller-Berghaus, G; Samama, M; Thiel, W (Thromb Haemost, 1987)