Hi Rafal,

Haven't had time to plot your curves manually, but here's the graph paper I would use. The green lines correspond to your step tablet actual densities... I find graphing goes faster when I have green lines for each x-axis step...

http://www.beefalobill.com/images/sensitometry-RL1.pdf

The top "film speed" scale is not calibrated to your setup. Cut it off and slide it left or right to get an idea of your relative film speeds.