i found this , but i have no idea if it is accurate or not , could it be used to make a spreadsheet like the one you made based on the jackson ratio ?
http://www.shellshack.co.uk/hibernating.php
There is another method of calculating whether your tortoises weight is sufficient for it to survive hibernation which some people claim is a more accurate method called the Bone Density Ratio.
The bone density can be calculated by obtaining your tortoises weight in grams and dividing it by the tortoises total straight shell length cubed. If the result falls between .20 - .25 then it is considered safe to hibernate your tortoise.
This calculation is easier than appears.
- Firstly turn your tortoise on its back and accurately measure the length of the plastron length in cm's.
- Multiply this length by its self 3 times (plastron length cubed).
- Weigh the tortoise in grams.
- Divide the weight in grams by the length.
- If the outcome is between .20 and .25 it's safe to hibernate your tortoise.