The distinguishing feature of this book format is its long extension of the leather cover along the lower edge of the book, which allows it to be carried by hand, or be tucked under the belt, held there by a large knob or hook incorporated into the overhanging leather. Judging by contemporaneous representations in paintings, sculptures, drawings and in verbal descriptions the majority was made between about 1450 and 1650, mainly in what is now Germany, the Netherlands and England. Only about two dozen still exist, making it a very rare witness to medieval life between six hundred and seven hundred years ago.