Your BC780XLT has a build in bandplan. This means that when you enter a new frequency into your scanner the mode and step will be selected from a pre-programmed list.
For your convenience, ARC780 also has a build in bandplan.
When you enter a new frequency in the software the mode and step are automatically selected.
You can easily change the software bandplan.
The zipfile you downloaded contains an example custom bandplan called 780plan.dat.
How can you use and change a custom bandplan?
Copy the file 780plan.dat from the zipfile to the directory where you installed ARC780.