@pierrot10 1 mm of rain over 1 square meter is 1 liter of water. Correct! One liter makes 358 tips so one tip is then 2,7932 milliliters that is correct. But rainfall mm/hr is 2,7932 * nbr of tips only if the area of the funnel is 1 square meter. Your funnel is only 55 square centimeters so you will only collect 55/10000 of the rain that falls on the whole square meter. The example you are using at the top of your post does not have the size of the funnel anywhere in the code.