https://en.wikipedia.org/wiki/Charango:

• Ronroco (also ronrroco): a still larger relative, essentially a baritone or bass charango, about 80 cm long with a 46–50 cm scale. It was invented by Gonzalo Hermosa, of the group Los Kjarkas from Cochabamba, Bolivia, in the 1980s. Ten nylon strings are arranged in five double courses. As with the charangón tunings vary, and depending on region and use the ronroco may be tuned a fourth lower than the charango (Argentine tuning); a fifth lower (Bolivia; Chile); or an octave lower ("Bolivian tuning"). The octave lower tuning is better acoustically supported by the larger body of the ronroco, and is more common on this instrument than on the charangón. The strings of the third (center) course are tuned an octave apart; strings in the other courses are usually tuned in unisons, though occasionally the fourth or fifth courses (or both) may be tuned in octaves. When courses four and five are doubled at the lower octave the ronroco is essentially no longer in reentrant tuning.^[20]

credited here