Hello Seth, The trend arrow is a 3 hour comparison which changes on every half hour. If you do not see the temperature trend arrow change, please try the troubleshooting steps listed below. Thank you.
To do a pinhole reset: (THIS WILL CLEAR ALL OF YOUR HISTORY AND YOUR SETTINGS)
Please verify that you are using a name brand (Rayovac or Energizer) standard alkaline batteries in the display unit. We do not recommend using anything that is heavy duty, rechargeable, store brand or Lithium inside of the display.
- Remove all power, AC adapter and batteries from the display unit. - Press and hold down the pin hole reset button, located in the battery compartment, for 20 seconds. - Plug back into AC power and insert recommended batteries. - Press and hold down the pin hole reset button for an additional 20 seconds. - Verify that the unit has powered on and once connection has been made, attempt to set time and date.