If your AcuRite® Optimus display unit or AcuRite NOW account is reporting inaccurate rainfall readings, the following procedure can be used to verify or improve the accuracy of the rain gauge on the AcuRite® Optimus sensor.

NOTE: The AcuRite® Optimus sensor comes pre-calibrated. The steps below are not required for a new sensor. 

To calibrate the rain gauge on the AcuRite® Optimus sensor:

Items Needed:

AcuRite® Optimus sensor, display console, plastic cup, pin, screwdriver

1. First, make sure the AcuRite® Optimus sensor is perfectly level using the built-in bubble level.
2. Place the display console close by so you can monitor it during the calibration process.
3. Make a pinhole in the bottom of a plastic cup. Hold the cup over the rain gauge and fill it with exactly 1 cup (8 oz.) of water, allowing the water to drip into the rain gauge. You should hear the internal tipping spoon "tip" as it measures the water passing through the rain gauge.
4. With each tip of the tipping spoon, the weather sensor records 0.01” of rainfall. The rainfall amount is transmitted to the display every 36 seconds, and you will see it update with a new total. If the tipping spoon tips more than once in 36 seconds, the total will increase by more than .01" with each update.
5. The cup of water should take at least 20 minutes to empty; a quicker period will result in an inaccurate calibration. (We’re trying to simulate a normal steady rainfall.) When the cup is completely empty of water, the display console should register 0.80".
   NOTE: We recommend performing this procedure multiple times BEFORE making any adjustments to the calibration screw to ensure adjustment is needed. 

If the rain gauge doesn't register close to 0.80" after performing this procedure a few times, you should adjust the calibration screw next to the tipping cup (as shown below). To access the calibration screw, grab the rain funnel from the side next to the leveling bubble and pull upwards and towards the solar panel to expose the tipping cup. Turning the screw clockwise will decrease the rainfall amount. Turning the screw counterclockwise will increase it.

Adjustment:

1. To adjust the rainfall reading by 2% turn the screw 1/8 of a turn.
2. To adjust the rainfall reading by 6% turn the screw 1/4 of a turn.
3. To adjust the rainfall reading by 9% turn the screw 1/2 of a turn.