Long RH1 key

[sarton]

I always wonder what the use is of the long RH1 key that controls a hole close to the head joint of my 10-key simple system flute.
Does anyone ever use it?

[dunnp]

Sounds like a trill key for high d (d'''/ e''') trill.

[sarton]

Thank you !
A bit difficult to reach for me if I want to keep my pinky on the Es key at the same time, but it works.