ACCESS/SQL: Calculating the difference between rows (not dates)

I looked through the questions here but didn't find one that suited my case.

I'm trying to write a query that will output the difference between rows

Here is a table:

ITEM     CYCLES
--------------------
itemA     5
itemA     17
itemA     20  
itemA     22
itemB     26
itemB     30
itemB     37

it is actually obtained by a query, and with an order by (item, cycles)

here is what I'd like the query to give me:

itemA 12
itemA 3
itemA 2
itemB 4
itemB 7

I have absolutely no idea how to proceed in SQL. Is it even possible ? or do I have to write a function ?

*****************************EDIT*********************************

I appologize for the lack of precision, and even some absurd mistakes. I was rushing out and wrote hastily :/
I'm analyzing item failures, and need to output cycles between failures.

ITEM column is just the item ID, and
CYCLES is the number of cycles the item had when the failure occurred.

And actually looking at it today I don't understand why I put that middle column (A,B,C...) which I don't have in my table.
And indeed, I don't need to output zero values, but there shouldn't be any anyway. I'll try the provided solutions and will get back; thanks for the answers !

Solution

Here's an updated solution, based on the changes to your question. Note that you'll need to change Qry to the name of your query:

SELECT Qry.Item, Qry.Cycles - (SELECT TOP 1 Cycles FROM Qry AS Q 
                               WHERE Qry.Item=Q.Item
                                 AND Q.Cycles < Qry.Cycles 
                               ORDER BY Q.Cycles DESC) AS Diff
FROM Qry
WHERE (SELECT TOP 1 Cycles FROM Qry AS Q 
       WHERE Qry.Item=Q.Item AND Q.Cycles < Qry.Cycles) Is Not Null
ORDER BY Qry.Item, Qry.Cycles;

This produces the following output:

Item    Diff
itemA   12
itemA    3
itemA    2
itemB    4
itemB    7

I assume that the 6 in your sample output was a typo, since 30 - 26 = 4.