Skic A., Szymańska-Chargot M., Kruk B., Chylińska M., Pieczywek P., Kurenda A., Zdunek A., Rutkowski K.:  Determination of the Optimum Harvest Window for Apples Using the Non-Destructive Biospeckle Method (2016 r.) Sensors 2016, Vol. 16, 661,