Negative curve is for PNP.. step size is programmable The bigger the output steps indicates higher hFE for that step input. hFE drops with increased current. Flat slope means perfect current source, non flat indicates leakage on current source. step space on output converted to mA divided by step size on input = hFE at that point vs Vce.. A very linear device has flat curves. A very high gain device has big steps on output.. For more resolution,, reduce input step size (mA) and number of steps.