Evaluating the difference of a list of numbers

Does anyone have any ideas that would help me solve the following. My users will do an API query which returns a list of numbers such as the following for example:

Im trying to extract the difference between each number in the list which would be 2.50 and save that in a data field for future use. Other occasions it may be a list of numbers that up steps in 0.50 multiples. Any ideas of an arithmetic action that could derive that from the API response list of numbers?

You mean the entire list will always have the same increment between each number?

Thats the issue. The API call returns a list of 80 numbers. Lets say the first and last 20 are in increments of 5 but the middle 40 are in 2.50 increments of which im trying to extract. If I can somehow grab the 40th number in and subtract it by the 39th I could derive the 2.50. The problem is the API response returns a list of those 80 numbers separated by commas in a text type format which doesnt allow me to run arithmetic on. I cant even seem to get the full list of numbers to store in the database. Step 1 API call. Step 2, make changes to a thing and store result of step 1 into a data field. When this happens it only seems to store this (verbatim): [object],"

Im sure ill eventually figure it out. Just one of those peculiar development issues.

I was able to figure this out. I had to switch the response type from json to xml and make sure the type when initializing the call was number. Step 1 initializes the call. Step 2; makes changes to a user. Xfield = Result of step 1’s response’ number #:40 - result of step 1’s response’ number #:39. It then stored the difference.