I go along with the generally accepted theory that the game measure is 33cm.
The third clue enigma 780 talks about ‘where you must by the compass and the foot.’
The ‘foot’ most likely refers to ‘pied du roi’ , and it the word ‘step’ in the title also hints at this measure. A common value was close to 33cm.
The visual shows a compass. The compass has a diameter of 10.5cm, which Max confirmed. The method to work out the perimeter of the circle = 2 x Pi x radius, where the radius = diameter / 2 = 5.25 cm and Pi = 3.1415, or about 22/7. So, the perimeter of this compass is 33 cm.
The 33cm measure fits very well with the measures mentioned in the book, to give neat whole numbers eg. 185km rather than messy numbers like 176.457889km!
Other ideas for the measure
Some people think the measure is the compass AND the foot, so 10.5cm + 33cm so 43.5cm.
The historic measure the ‘foot’ had many variations over the centuries, as this French Wikipedia page devoted to the ‘Pied’ shows. The 74 cm foot is used by some owl hunters.
The word “measure” appears in the puzzles. 500 , 420 and 650 , as well as an additional clue : ” For good measure, there’s only one in the book ” .