How do you measure rainfall in amounts as small as 0.01"?
Contrary to suggestions by some, it's not done by elves using really small rulers! It's actually done using what's called a tipping bucket rain gauge. Picture a device that looks a little like a teeter totter from our grade school playgrounds with a cup-like shape on either end. Each time the upper arm fills with a given volume (and therefore weight) of water, it tips and empties. The 'cup' on the other end is next to fill...and tip...and empty. The gauge mutliplies the volume of each tip by the number of times the device tips to calculate the total. That allows calculation of very small amounts of rain.