Hello
I´m Matias From Buenos Aires, Argentina.
I have a Acurite Atlas and it has the same issue. It shows a lower UV Index (about 40 - 50% less).
The Customer Support wrote to me by chat the following procedure for this issue:
Verify that you are using a fresh set of batteries. The battery expiration date should be at least 6 years out. Batteries can lose 3% of their power or more every year in storage.
Bring both the sensor and display unit indoors and position them side by side.
Remove the batteries from the sensor.
Go to the main menu by tapping the "MENU" button. The "MENU" button is the three white horizontal lines in the upper left-hand corner of the display.
Tap the "SENSOR" option from the menu.
Tap "REMOVE A SENSOR". It will show you a picture of the Atlas sensor.
Tap "DONE".
It will ask you to confirm removing the sensor, tap "YES".
It will ask you "Are you sure?", tap "YES".
The display will revert back to the previous screen. Tap the back arrow in the upper left-hand corner of the display to return to the main menu.
Tap "FACTORY RESET".
You will receive a prompt asking if you want to reset to factory settings. Tap "YES".
It will ask you "Are you sure?", Tap "YES". The display will reset itself and go to the main AcuRite logo screen.
You will now be able to set up the display up by following the on-screen prompts.
Once that is completed, put the batteries back into the sensor.
Go to the main menu by tapping the "MENU" button. The "MENU" button is the three white horizontal lines in the upper left-hand corner of the display.
Tap the "SENSOR" option from the menu.
Tap "ADD A SENSOR".
The display will look for your sensor and show a picture of it when it is found asking if you would like to add it. Ensure that the designation in the description matches the channel that you set your sensor on. Tap "ADD THIS SENSOR".
The display will revert to the previous screen. Tap the back arrow in the upper left-hand corner of the display twice to return to the main screen.
Let both sensor and display sit side by side to establish a connection. (Leaving the units side-by-side for 30 minutes will allow you to verify accuracy by comparing the indoor and outdoor readings shown on the display.
After a connection has been established, the sensor can be placed outdoors.
Did Anybody do it?
Thanks in advance
Matías