Thank you very much. That was very clear. In the mean time I searched around on google. The property of this proof of work is that the duration of the work is

Thank you very much. That was very clear. In the mean time I searched around on google. The property of this proof of work is that the duration of the work is random. How is it possible to know the average work time duration, without doing the measurement ? Is it possible to provide a work time limit so that if a client has really bad luck and can't find the solution in that period can he can issue another question ? From the ur perspective, this varying work time duration may be an unpleasant experience.