Gravity Analog Dissolved Oxygen Sensor SKU SEN0237 Calibration

I have watched YouTube videos on how to calibrate this DO Sensor, but I have also seen how to calibrate it on the DF Robot Wiki itself. Should I just pour in the 0.5M NaOH solution directly into the membrane cap, or do I need to add 1-2 drops of Glycerin per 100mL of 0.5M NaOH I bought (so 500ml would be 5 drops)? Please help, as the YouTube video shows just using the 0.5M NaOH straight up and skipping the Glycerin step (while still working). Thanks!