What does the middle position on the altitude source select switch do?

What does the middle position on the altitude source select switch do? The top position is barometric pressure and the bottom is radar altimeter, but there's an unlabeled middle position. Altitude hold still works when the switch is in the middle position, so does it function as auto source select (below 300m is radar, above 300m is baro)?

The center of the BR/RD switch behaves like the last position (BR or RD) which was selected and had an altitude capture event (collective brake squeeze or altitude channel engagement).

If you use RD and switch directly to center position it will act like RD. If BR is in use and switch is placed in center it will act like BR. If BR is in use and the switch is placed in RD and then center it will act like BR (because while the switch was placed in RD, no capture event occurred while it was there).

The behavior of the system doesn't change in any case until a capture event. E.g. if switch is moved BR to RD, system will still act like BR until the next capture event occurs.

If RD captures above 300m height then the channel will attempt to fly at 300m when the signal resumes. If the channel is following a lower height (e.g. 200m) and flies out of signal, it will resume 200m when signal resumes.

Thanks, very helpful!