Pix4D Essentials Workbook Prescription Values

I am going through the Pix4DFields Essentials course and have a question in regards to the Prescription Values. It seems that the values I am being asked to enter are quite random in nature. So the question is how do you go about defining or calculating the prescription application values for variable rate application? Is this by product definitions or just something that is known? Is there a reference for product application values that would be used in Pix4dFields? I know it may be a dumb question but I am a bit new at this and can’t seem to figure out where this information is coming from.

Thanks!