How does max flow calibration work?

[Edzi11]

Like the title states, how does this calibration work? I ask because if i do the test and it shows that my max flow rate is 18mm^3 but in the slicer it shows that when printing the speed is only reaching 100mms how does this translate to when the infill is printing at 300mms? Im just confused on how your testing for max speed but using slow speeds to do so.