Hi guys ELF means the target rpm is not stored in the ram data chip so is deleted after you power off ESC , so the next flight the ESC has to relearn the target rpm , so rpm can be different due to battery state of charge, in the other mode governor store the max rpm of the motor will be stored in the chip set ready for next flight and head speed will be the same no matter state of charge of the battery ( dont forget voltage cut off will kick in sooner on a low battery)
The hobby king YAP does the same use a battery that is charged NO more than 4 volts a cell, remove the main and tail blades , now put ESC into store mode run heli to full throttle till motor rpm kicks , the esc has now learnt the max of the motor , now refit blades charge battery and set transmitter to 80% throttle the governor will now use the rpm left to keep the 80% head speed for the full flight
The YAP also has active free wheeling so this help to give longer flight times as the motor is powered as its needed in flight ( this works so fast your never know its doing it ) my 500 pro is getting 10 mins on a 6 cell 3000mah