You can’t program the BC 245XLT to track the Harford County TRS, since the system is APCO 25 (Digital). APCO 25 is also known as P25. Harford County is on 800 Mhz, but need to upgrade your scanner equipment to received this system. You need the Radio Shack (RS) PRO-96, RS PRO-2096, Uniden 396, Uniden 996, GRE PSR500, or the PSR600. These scanners cost around $500, but some of the older digital scanners can received this system and can be purchased used. 800 Mhz trunked radio systems don’t require base and offset to be program in order to track the trunked systems.
About the only thing that can be received in Harford County is Fire Dispatch on this scanner. Fire Dispatch is on 460.600 Mhz. The 245XLT will track Baltimore and Anne Arundel County TRS for now.
Hope this helps you, even if not the answer that you would have wanted.
Larry