They say you can take any cylinder shape container, a bucket or jar etc and **as long as the diameter is the same through out** all you have to do is measure the amount of water at the bottom to get a total.

They are right, if you measure the

**depth** of the water at the bottom as Mattk says. But it doesn't even have to be a cylinder: anything with vertical sides will do, like a box.

Problem comes when you try to measure depth down to 0.01" in the bottom of a can or box, so it's best if you can funnel the rain you collect into a narrower container where it's easier to measure small amounts (like a CoCoRaHs gauge) or into a tipping bucket gauge - and that's where the math comes in

And speaking of math: over here we measure rain in millimetres (mm) but in, e.g., Belgium they measure in litres/square metre (l/mē). The number you end up with is exactly the same.