In this case, it would be fastest to use your ruler to get some of the X and Y points for the three Pa curves. Store them in Matlab vectors. Then run an smoothing operation if needed.
x = [0.1 0.4 0.7 0.9];
Pa5m = [0.25 1.5 1.25 0.25];
Pa10m = [0.6 2 1.5 0.25];
Pa20m = [1.2 2.5 1.75 0.25];
xq = 0.1:0.05:0.9;
Pa5m = interp1(x,Pa5m,xq,'spline');
Pa10m = interp1(x,Pa10m,xq,'spline');
Pa20m = interp1(x,Pa20m,xq,'spline');
The rest of the plotting is straight forward once you have them in vector form. There are also other options for interpolation method that may work better for your problem.