That's a good question Steve. Here's a long answer, some of which you probably know already but I'll be thorough for other people that might not know.
There are two ways to cook sous vide, one is based on the thickness and the other is based on the tenderness.
Cooking based on thickness is how PolyScience, Baldwin, and Nathan started out as they did research on food safety. Cooking sous vide based on thickness basically tells you the minimum
time you can cook a piece of meat to ensure it is safe and comes up to temperature in the middle. It doesn't take into account tenderizing time or any other factors. It's often used by restaurants or home cooks who want to minimize cooking time and are using tender cuts of meat that don't need the tenderization.
Cooking sous vide based on tenderness takes into account how tough a piece of meat is and how long it needs to be cooked in order to make it appealing. So a chuck steak needs to be cooked a lot longer than a filet, even though the are both safe after the same amount of time. As long as the minimum cooking time is met for the temperature used then it's completely safe to eat.
Both sous vide methods definitely have their uses. Thickness-based is great for very tender cuts cooked by people who need them done at an exact time. Tenderness-based is great for longer cuts or people that have a range of time that they are interested in.
In order to keep things more simple in our sous vide app
we decided to stick to the tenderness based method as the majority of home cooks seem to use it. One of the hardest parts of sous vide is also knowing how long to cook something in order for it to taste good.
For good charts with the thickness method you can look at Baldwin's online guide
. We will also be releasing an update with the thickness information in a month or two, and releasing a printable guide. I'll keep you posted about them.
I hope this helps answer your question.