Hi Christoph,

This is your data as I would interpret it. Notice the ASA triangle. The tip of the triangle at the toe of the curve that fits that triangle, is where I marked 400, the ISO speed of that film. The other speeds marked are based on the point where their curves reach 0.10 above Base+Fog. The relative speeds can be read directly above that point off the chart pasted in the middle of the graph.

HP5
N+1 CI .72: ei 640-800 @ 16'
N CI .60: ei 400 @ 11'
N-2 CI .45: ei 320 @ 8'
N-3 CI .37: ei 250 @ min 5'30"
CI .25: ei 200 @ min 4'