extrapolation of logarithmic graph

Question

I need to extrapolate the following graph.

Could someone help me with the formula for the logarithmic graph?

Answer 1

1. read two points from the graph, for example (1,200) and (1000,10) (those are the points at the right and left border).
2. Calculate the log10 for each: (0,2.301), (3,1).
3. Use those two points to fit a line through - y = ax+b => 2.301 = 0a +b; 1 = 3a +b => the first one conveniently collapses to b=2.301, and using this in the second one gives a=-1.301/3=-0.434

So your line is y = -0.434 x + 2.301, and if you want it back in the base variables log(p) = -0.434*log(t) + 2.301