What are the wiring requirements and terminal designations for the Honeywell thermostat?

The TH6210U2001 uses 18- to 22-gauge thermostat wire (shielded cable not required) and includes specific terminal designations: R for 24VAC power from heating transformer, Rc for cooling transformer power (joined by slider tab for single transformer systems), Y for compressor contactor, W for heat stage 1, G for fan, C for 24VAC common, and O/B for changeover valve on heat pump systems. The R slider tab should be set to position 1 for single transformer systems or position 2 for two transformer systems. Terminal C is optional if batteries are installed but recommended.