From inside (document excerpt):
RTH6400D 5-1-1 Day Programmable Thermostat. Easy-To-Use Programming For Weekdays, Plus Saturday and Sunday. Free PDF Brochure.
KEY FEATURES:
• Large backlit display
• 4 programmable periods per day
• +/-1° F precise temperature control
• Auto change from heat to cool
• Exclusive Honeywell Smart Response Technology
• Temporary and Permanent hold settings
• Fahrenheit or Celsius temperature display
• Short cycle protection
• Natural language (no symbols)
• Soft-touch button interface
• Room and set temperature display simultaneously
• Easy-access battery compartment
COMPATIBILITY CHART:
24-VOLT HEATING AND AIR CONDITIONING SYSTEMS:
Single-Stage Heating and Cooling – Yes
Multi-Stage Heating and Cooling – No
Heat Pump without Auxiliary Heat – Yes
Heat Pump with Auxiliary Heat – No
Gas Fireplaces – Yes
Heating Only – Yes
Cooling Only – Yes
Electric Baseboard Heat (120-240 Volts) – No
Source: honeywell.com