Complex sentence: He is also an inventor (at about 1980) of local Polish grading system of free climbs, an opened scale, called "Kurtyka scale" or "Krakowska scale".
Split into simpler sentences: He is also an inventor (around 1980) of the local Polish grading system of free climbs. This system uses an opened scale, called "Kurtyka scale" or "Krakowska scale".