Analysis of information sources in references of the Wikipedia article "Parmak Hatırlatıcısı" in Turkish language version.
When we close the hand there are four projecting knuckles of the four fingers, with depressions between them. If we give the knuckles and intermediate depressions the names of the successive months, recommencing from the first knuckle, after having once gone over them, we shall find that the months of thirty-one days are those which fall upon the knuckles. Also, in easier words, the gaps between the knuckles indicate months with not 31 days but 30 (excluding February which is 28/29).
