The steirische harmonika is often confused with an accordion, while this instrument is clearly not an accordion. This instrument is a member of the pull bag family which consists of a large number of different instruments around the world.
The steirische harmonika played by Heidi-Rose comes from the Alpine countries and is a diatonic (= change tone) instrument.
The basses are Heliconbass (Helicon) that give a very specific yuba-like sound that makes them instantly recognizable.
Diatonic
Change tone = a term used to indicate that a key sounds a different tone when the bellows closing and opening.
This means that there are 2 different tones under each button. If you hold down 1 key, a completely different tone will be heard with an openings bellows than with an closing bellows.
A few examples:
push = c (do) -> pull = D(re)
push = E (mi) -> pull = F(fa)
As a result, The G (sol) note is out of place in a musical notation as where normally a G (sol) is.
That is why there is NO key as a sign on the staff. In the notation of a steirische harmonika, the G (sol) was noted at the site of a B (si).
The musical notation for a steirische harmonika is officially called: Griffschrift. (In English: handles writing).
Helicon (Musical intrument)
The Helicon is a brass instrument from the Tuba family. A helicon is closely related to the sousaphone but does not have the cup facing forward and lacks the gooseneck construction for the mouthpiece. Most instruments are tuned in B flat, to a lesser extent in a E flat or F. Like the sousaphone, the instrument is carried on the shoulder with the head held by the windings of the instrument.
The role of the instrument had largely been taken over by the sousaphone, but it is still widely used in Central and Eastern Europe.
The steirische harmonika is also popularly called wiener or steirka. Heidi-Rose often calls her instrument wiener.
Repertoire
Heidi-Rose has an enormous repertoire on her steirische harmonika. Her entire repertoire is available for inspection here.