In this mode, both hands play only lower keys.
This mode is no longer without errors like the upper keys, but is almost error-free with about 90% correctness. The right foot must sometimes leave the right pedal, if the sound becomes too strange. It is useful to play with the left hand accords and the right hands with a melody or use both hands melodies like in the Barock fugues.
The octaves with only upper keys have 7 different keys. So one can get 7 different scales by using different base keys in playing. The 7 scales were used in the Renaissance time, but got lost in Barock, when restricting scales to only major and minor scales.