F0 value calculation

i have a question regarding calculation of F0 value.
For calculating F0, every value is based on values given on Biological indicator report like N0 , D,and for sterility assurance 10-6 it is log 1.
so the question is that how it is related to the our in-house autoclave as for calculating F0 value we didnt take any value from our in-house autoclave.
For Eg: Suppose we have 2 autoclaves having different capacity (240 ltr and 50 ltrs.) both takes different total sterilization cycle time i.e.,one and half (hold time 30 min) and 1 hours(hold time 15 min) to complete. But as per Biological indicator the calculated value of F0 is 10 min. so how we correlate it.