can a quickbase show on the dashboard a comparison bar chart from 2 tables in the same app?

You cannot make a report from two different tables of data, But...
We could get the data (or at least a count) from one table to another.

Can you describe your current set up a little more, are there any tables that are connected to both of your device tables?

I was thinking that I might have to do that.  I do not currently have both tables linked to a 3rd table.  The Device tables *is* linked to another one, but that's for a different purpose.  The Allocation table is not linked to anything at this time.  The one table that shows the devices allocated just has the Department Name, Contact Person, Device Name Example (this shows anyone creating a new device how to name it), and the Number of Devices they should have.  The other table is a list of every device, Serial Numbers (2 different kinds), Asset Tag number, Device Name, Hardware Address, Location, Last Seen, and 22 more fields that don't really mean anything for this purpose.  I'm thinking that I would have to create the 3rd table (AllocatedVsActual) that is linked to the Allocation table's Department Name and Device Name Example, and create a formula that links to the Device List table to count the number of devices with a similar name.  Then, I guess I would create a report that will show both sets of numbers on the from the AllocatedVsActual table on the dashboard?

Just a note on side by side bar graphs.

It compares the the same data, but is classified in a different category.
For example, 
So if your dollar value was in the same field, but you classified the record as revenue or expense, you could then build a side-by-side bar graph.  One bar would be expense and the other revenue.

In your case, you'd have to have your device records all on the same table, with them classified as assigned, or available.

In this case it still wouldn't show a total allocated vs. actual, but rather it will show assigned vs available.

Overall, it sounds like you might need to re-architect your app/data a little bit.