This item defines the RPM at which Boost Timing (you specifically set) is applied. Example, if you set Boost Timing to 10 degrees, the Boost End RPM to 15000, then the ESC will activate the Boost Timing of 10 degrees when the RPM goes above 15000. The ESC will adjust the Boost Timing accordingly as per the actual RPM when the RPM goes below 15000.