Sun Weather Page reader Emily Johnston writes with a question about why her rain gauges don't agree with each other:

"I have 4 cheapy rain gauges, two of which agree; one is hard to read, so I'm guessing; and the last is totally out of line with the readings of the others. How can I calibrate these (or at least one of them) without some sort of fancy equipment?  Is there a rule of thumb relating the cross-section of the collector with inches of rainfall? Or should I just add up all the numbers and divide by 4? (I really don't want to do that.)  - Emily Johnston, Westminster, MD"

Well, Emily, I think you've answered your own question. Your problem is that you are using at least two "cheapy" rain gauges. Like anything else, you get what you pay for. Some rain gauges are made with some care and precision - which costs money - while others are made cheaply and consequently without such precision. You might as well use a jelly jar and a plastic ruler.

I would say the odds are that the two gauges that agree with each other are somewhere close to accurate. The one that's hard to read is badly made; a scientific instrument has to be readable. And the fourth, which seems to be "totally out of line" is most likely just badly calibrated.

When you lift the veil of mystery - and all the fancy technology - the truth is that measuring rainfall is pretty simple. Real meteorologists assure me that an inch of rain really means an inch of rain. So it doesn't really matter whether your gauge is a beer glass or a kiddie pool. So long as the sides are vertical and the bottom is flat, if the clouds drop an inch of rain on the yard, you should get an inch of rain everywhere.

Professional instruments, of course, are usually far more complicated. The "standard" gauge used by the weather service - invented over a century ago - is a cylinder 20 centimeters (almost 8 inches) wide at the mouth. It's actually a funnel that sends the raindrops into an inner cylinder that is 50 cm tall. Its cross-sectional area is exactly one-tenth that of the mouth of the collecting funnel. But it's not as arcane as it sounds. By concentrating the collection area in the inner tube, forecasters can stretch or exaggerate the vertical dimension of the accumulated rain. That lets them measure the depth more precisely with a specially calibrated scale - usually to the nearest 1/100th of an inch.

The gauge on my WeatherDeck is a "tipping bucket" instrument. The rain from the funnel-like collector drips into a little bucket inside the contraption. When the bucket fills and gets heavy enough with the accumulated rain water, it tips like a seesaw, dumps its water and brings the second bucket under the funnel. The cycle repeats as long as it rains. Each tipping action sends a wireless electronic signal, which registers as 0.01 inch of rain on the console in the house. A hundred tips equals an inch of rain.

But there's no need for most of us to invest in that kind of instrument. There are well-made rain gauges on the market that are simple plastic cylinders with carefully calibrated measurements on the outside. An inch of rain fills the cylinder to the one-inch mark.

Your options would seem to be these: Fill the one you can't read with water and stick a flower in it. Throw the outlier away. And use one or both of the two that agree. We'll assume that if two inexpensive gauges agree, there's at least a chance that someone at the factories got it right.

Or, if you need a rain gauge for some serious purpose, throw them all away and invest in a good instrument. One place to start looking would be Ambient Weather, which offers gauges from a variety of manufacturers on line. Prices seem to range from about $10 to $35.  But look around. And this time, don't go "cheapy."