Calibrating the Pro2 Double Spoon Rain Collector

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The non-metric version of the rain collector is calibrated at the factory so the spoons tip (and records rainfall) for each 0.01″ of rain. The metric version is calibrated so the spoons tip for each 0.2 mm. To adjust the calibration slightly, use a 3/16” (or 5 mm) wrench to rotate the adjustment screws which are located underneath the tipping spoons. The adjustment guide embossed in the platform shows how far you must rotate both screws in turn to effect a 1% and a 2% change. Moving the screws in the positive (+) direction causes the spoons to tip more times (i.e. give a larger count) for a given amount of water.

Note: Modify both adjustment screws by the same amount.

To check the accuracy of the rain collector, compare the Davis rain collector with a tube type rain gauge. Use a rain gauge with an aperture of at least 4 inches. Any smaller and the readings obtained may not be accurate. Place the tube type rain gauge directly next to the Davis rain collector. Compare the totals on three storms to determine whether your rain collector needs calibration and by how much. Adjust the screws to fine-tune the reading for the next three storms if necessary.

Note: Avoid comparison to rainfall readings obtained from television, radio, newspapers, or neighbors’ readings. Such readings are not an accurate measurement of the weather conditions in your specific location. The rain collector is carefully tested at the factory to conform to the specifications listed in the back of this manual.