Workflow: Calculate Value from Different List

Question

I've been hitting my head against a wall for a few weeks trying to figure this out.

I have two lists: The first has a list of books with a column of the quantity of the books available (InfoStationContentList). The second list (TestCheckOut) is a supposed to work as a "checkout" list, and has the option to look-up the Book Title from InfoStationContentList, and submit an item to have the book delivered. I have 2 look-up fields in TestCheckOut list; One of the Content Title (the book) and the second with the Quantity available. I have attempted (unsuccessfully) to create a workflow where If the Quantity in TestCheckOut (look-up field) is zero, the workflow (or checkout is rejected). HOWEVER, If the Quantity is not zero, it will subtract one from the InfoStationContentList quantity, thus updating its availability. Here's what I have so far:

I understand I will have to perform a look-up on the Title to do the calculation, but it still will not subtract 1 from the Quantity in InfoStationContentList when the workflow is completed. I've searched the other questions on the form, and tried to set up my look-up similarly, but have not had luck. Any insight? I appreciate the help! FYI: I'm using SharePoint 2010 and SharePoint Designer 2010.

Answer 1

After you output the subtracted value to Variable:calc1, you have to do an Update list item action on item in InfoStationContentList where titles match and set the value of Quan to Variable:calc1.