How to expose the quantity of list items to an action?
You have to create a new variable BEFORE your loop.



And then select the type of variables in that list. For your example, perhaps a list of decimals?



Be sure to give it a good custom name for your loop:



Then, in your loop, you can add a new variable to an existing list:



Then, after your loop, you can access calculation results:



Note, that if you don't know explicitly which in your loop you want, then you will have to loop through your new calculation results and use a condition rule to return the one you need as (yet another) variable.