was the probability of up or down probably you know in principle you could think about if first principle say well the air flow around this thing what might happen and so forth not going to be easy to come up with a very precise number so how do we get this parameter then to know probability of up versus down what we can run an experiment imagine we do it 10 times and with this as the results we get we see it's up eight times and down twice if that's the outcome of our experiments that we might just say well probability of up is 0.8