Hi folks, it. Looks like my bucket is under reading, I have a climet 100mm manual gauge and after the storm today the climet was about 2mm more than the Davis, I also have another Davis bucket that is modified to work with my OS station and that too is under reading compared to the climet.
Where do I go from here, I read somewhere about turning those screws but I can't find anything at the minute and there's nothing in the manual.....
Per Davis manual below:
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. (See “Rain Collector Internal Components” on page 2.) 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.
© Davis Instruments Corp. 2015, Product Number 7857, “Rain Collector”
WheatonRon editorial comment. Before calibrating, make sure the gauges are level, approximately the same height from the ground, and are as close as possible to each other and don't calibrate based on a single rainfall! Use at least three storms and then average them. All this being said, getting all three of your gauges to measure rainfall in a single storm exactly the same is highly unlikely as a result of wind, nearby trees, etc., and maybe most importantly, automated "tippers" like the VP2, normally underreport rain during heavy rainfalls as they have trouble keeping up with the volume of rain falling. I have 4 gauges and they rarely read the same--it is the nature of the beast. However, if a large rainfall occurs and Station A reads .96", Station B .94", Station C .97" and Station D .93", I would be very happy and view the differences as insignificant. But when I get results .96" at Station A, .68" at Station B, .54" at Station C, and 1.06" at Station D--those are unacceptable differences requiring calibration! One final word of caution--once you decide to begin the calibration process, make sure both screws get turned in the same direction using the same number of turns or you will never fix the issue and will likely be worse off. In other words, if you turn the first screw clockwise one complete turn--make sure the other screw is turned clockwise one complete turn--use a marker, if necessary, to keep track of your process!
