Would a LOD Exclude help me?

Evening all,

First of all I have made a sample of workbook and published it to Tableau Public here is the link - https://public.tableau.com/views/WirelessdbExample/Sheet1?:embed=y&:display_count=yes&publish=yes

My question is this: I am trying to get my data correct and I am fresh out of ideas.  Here's my situation - I have developed a database using MS Access that houses and manages a wireless program that reports on both inventory and monthly costs.

Here is what I am trying to do: 

     Show the current inventory which is for the current month i.e. each device in the database should = a count of 1.

     Show the monthly costs by month.  So for each device you could have a count of 12 as you would have one record of cost for each month.

Seems pretty simple right?!?  I am pretty new at this haven't figured it out.  The sample is the same structure but the data is changed to protect the innocent.

So I joined the table in the database and brought in the tables.  Everything is an inner join as they all are connected via a one to many relationship in the database.  So far so good.  Here's where the problems start - when I try to show a count of devices for an inventory, I get a count of 12 - one for each month.  I tried a LOD expression (I am just learning about these) with an EXCLUDE MONTH and that didn't work.

I joined to the data base twice.  Once with the cost and once without the cost. Additionally I added the deviceID at an ATTR.  I think that is the right way to go but I get some stray values when you get a few months in the viz.  Part of the issue is the underlying dataset I have to actually work with.  What I am actually trying to do is to connect the device ID from the inventory to the cost but the number never seem to equal each other when I verify the viz and the data contained.

Help!

Thanks,

Scott Carman