I make it medium ground. It depends how long you process the oats. I think this is splitting hairs a bit as I doubt you would really know. But how can I prove it to you? I can only suggest that perhaps @Kake Lover (or me) makes a batch of parkin using both for comparison.Depending on the parkin recipe milled porridge oats do not work properly. Proper parkin requires medium ground oatmeal not finely ground. It does make a huge difference.