Mountain drive crank + BSR 3 speed 2 planetaries , 3rd to 4th is also a double shift..

Crank low range , up to high range, + hub from high 3rd, to low , 1st, , and the inverse 4th to 3rd.

can be done simultaneously , at a slow bogged down in too high a gear on a hill and chainrings barely turning,

Because both are planetary gears , the chain never has to be pushed off 1 cog or chainring to another..

Fwiw R'off does a similar double shift between 7th & 8th.. sequenced internally.


[my father, right after I went in the US Navy , 1966, (HS grad,> viet nam war conscription time) , gave my 3 cubed bike

to the son of a family friend , who promptly let it be stolen]