feed state is not detected because it did not last long enough the accumulate volume is also compared to a validation volume as at 66 the mask volume marks the beginning of a validation window and the calibration volume marks the end of the validation window during recursive loops of this switch event detection the accumulated volume is increased until it enters the validation window and the controller begins looking at the state of the regulator valve if the regulator valve is detected to be in a full feed state during the validation window possibly because it entered the full feed state during the mask window then the process begins to recursively follow branch 72 branch 72 records that the full feed state existed during the validity window and further whether the full feed state existed at the start of the validity window if the valve switches back to the regulating state after having reached full feed then the oncoming fill phase is exited as at 68 and step 70 however if the regulator valve does not switch back to the regulating state within the validity window then the process begins recursively taking branch 74 branch 74 records that the regulator valve did not switch back to the regulating state before exiting the validity window it also records in which state the regulator valve exited the mask window thus separate validity flags are maintained by loop branches 72 and 74 to indicate three observations whether the full feed state was noted after the beginning of the validity window whether it was initiated before or after the beginning of the validity window and whether a switch back to the regulating state was observed before the end of the validity window fig4 illustrates the switch detection procedure that occurs when the transmission.