There are a couple of ways to do this depending on your need. The simplest tends to be using a combination of the TracerPlus AutoFind option along with the TracerPlus Increment Variable settings.
The idea is that you would configure the Barcode field to turn on "Auto Find on Scan" in the After Scan field options.
You would also configure the Qty field to be a *Variable* type and set to Increment.
Yes. In the case of the original question, this is what the user had wanted to do. Keep in mind, the INCREMENT variable allows incrementing by a settable number; the default is 1 but can be set to any value. If you wanted to sum things in different ways, there are other options. Using the calc functions and lookup/Update Source options allow a lot of different options like subtotaling, etc. Did you have a seperate scenario in mind?