Researched and devised by Dr. Oliphant Jackson, the Jackson ratio is a method of determining whether a member of the

tortoise Tortoises () are reptiles of the family Testudinidae of the order Testudines (Latin: ''tortoise''). Like other turtles, tortoises have a turtle shell, shell to protect from predation and other threats. The shell in tortoises is generally hard, ...

species '' Testudo graeca'' or ''

Testudo hermanni Hermann's tortoise (''Testudo hermanni'') is a species of tortoise. Two subspecies are known: the western Hermann's tortoise (''T. h. hermanni'' ) and the eastern Hermann's tortoise (''T. h. boettgeri'' ). Sometimes mentioned as a subspecies, ...

'' is maintaining its optimum bodyweight, which is necessary for a successful

hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...

Calculation

The Jackson ratio is calculated by taking the weight of the tortoise in grams and dividing it by the cube of the length of the tortoise's

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

in centimeters. This is essentially a value of the density of the tortoise in g/cm³. The optimal value for this ratio is 0.21 with a range of 0.18–0.22 being acceptable for hibernation. Values significantly less than this indicate an underweight tortoise and larger values are indicative of overweight tortoises. The Jackson ratio is expressed as a graph of minimum and optimum weights for a given carapace length. This exhibits the same principle without the maths.

References

* * * Tortoises Turtle terminology {{Turtle-stub