Our power meters are a great way of measuring progress and managing our efforts.
To be sure that your data is accurate though you have to calibrate your power meter every day. Temperature changes will affect the power meter's accuracy. With this in mind it becomes important to consider when you calibrate.
If you are ridnig outdoors and it is cold you will need to calibrate before you ride, and then probably again once you have been outdoors for 10-15min, giving the power meter a chance to adjust to the temperature change.
You can do the calibration on your Wahoo or Garmin head unit.
How you access the calibration function is unique to each head unit. You can do a Google search:
calibrate power meter (enter your head unit). This should get you instructions.
Making this part of your pre-ride routine will ensue that your data is accurate and so comparable over time.