Jackson ratio Researched and devised by Dr. Oliphant Jackson , the Jackson ratio is a method of determining whether a member of the tortoise species Testudo graeca or Testudo hermanni is maintaining its optimum bodyweight , which is necessary for a successful hibernation . The length of the carapace is measured in millimeteres , and compared to the weight of the tortoise in grams . Plotting the two values will show if the tortoise has a weight/length ratio optimal for hibernation . External links http : //www.slowcoach.org.uk/care/jackson/jackson.html  This article about a turtle is a stub . You can help Wikipedia by expanding it . Categories : Turtle stubs | Tortoises 