Speed Transition (IAS - Mach)

In this video, I cove when the transition from IAS to Mach in climb and descend, is performed by the FMC.
The answer that I get most of the time is Flight Level 250, or 290, and the answer is neither.
The FMC performs the change over in the speed from IAS to Mach in the climb when the two target speeds are equal.
And the opposite is true during descend it will change from Mach to IAS when they are equal.