YOUR rain-meter is in error... perhaps!


for years now i have taken some ‘pride’ in recording rainfall…

the thumbsuck test i just did to verify accuracy is to get the mm diameter of the catchment opening, get the equal amount of water in grammes [ml thus, kitchen scale?] pour it into the rain meter and it should be at the 10mm mark…

All this talk about mm and ml, but no mention of the area of the opening, which I doubt will be the same for all rain meters? Show your workings!

great, i just knew there is something amiss here, the top diameter is 13.3cm

edit in bold :slight_smile:

Ok, now I’m going to have to see a picture of how you managed to get that measurement.

took top, traced outline, got centre, doubled radius… took inside of pencil line :thinking:

Well then your hands must be absolutely massive (referencing the photo above)!

please see edit above, the diameter should read 13.3cm which also brings my hands back in proportion…

Ok, you made me go outside. I measure mine at around 127.5mm in diameter. That equates to about 127.67cm². I filled it to roughly the 10mm mark, and weighed the water at 124.5g. So 9.75mm equivalent. I’d say that’s within reason for accuracy (it’s probably more accurate than my eyeball filling).

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sorry for the burnt calories @_a_a_a and thanks a lot for helping me! it turns out i have to at least tell the guys at the shop not to worry… indeed no train-smash

No worries, I have plenty of calories I can afford to lose.

Hmmm? From your dimensions, 10mm of rain should be 139g of water, not 100g?

i should have asked chat gpt - at least facts do not seem to confound it - the right question must be asked though…:laughing:

hi, if a rainmeter has a round top catchment of 13.3cm and is cone shaped with a lenght 34cm at which mm mark will 100ml of rainwater be


To determine at which millimeter mark 100ml of rainwater would be in a cone-shaped rain gauge with a round top catchment of 13.3cm and a length of 34cm, we need to calculate the volume of the cone at various water levels.

The formula to calculate the volume of a cone is given by:

V = (1/3) * π * r^2 * h

where V is the volume, π is the mathematical constant pi (approximately 3.14159), r is the radius of the rain gauge catchment (half the diameter), and h is the height or water level.

Given that the round top catchment has a diameter of 13.3cm, the radius (r) would be half of that:

r = 13.3cm / 2 = 6.65cm = 0.0665 meters

Now, let’s find the height (h) at which the volume of the cone would be equal to 100ml (0.1 liters) or 0.0001 cubic meters:

0.0001 = (1/3) * π * (0.0665)^2 * h

Simplifying the equation:

0.0001 = 0.003491 * h

h = 0.0001 / 0.003491

h ≈ 0.02865 meters

To find the water level in millimeters, we can convert the height from meters to millimeters:

0.02865 meters * 1000 = 28.65 millimeters

Therefore, approximately at the 28.65 mm mark, 100ml of rainwater would be in the cone-shaped rain gauge.

Please note that this calculation assumes the cone shape remains constant and does not account for any variations or irregularities in the rain gauge design.


I think it’s trying to calculate how high the 100ml will fill the cone of the water meter. Not the equivalent measured rainfall mm. But even so it will be wrong because it’s assuming the cone ends in a sharp point, which it does not.

I’ll play around with it to see if stating the question differently we could get a better answer, it has access to all the right formulas…

You have to give it the correct info and ask the right question:

If a rain meter has a round inlet with a diameter of 13.3cm, how much water will it catch if it rains 10mm?

As a bonus, if you ask it the water level, it gets it wrong:

If the rain meter has a conical shape, with the top diameter 13.3cm and the bottom diameter 1cm, what will the water level be in the meter?

[long calculation, same as below but wrong-way round]
Therefore, the water level in the meter would be approximately 1.053 cm.

What will the level be if you swap the top and bottom diameters?

What is the 500th digit of Pi?

ChatGPT: 8


ChatGPT: Sorry, I was wrong. It is 5.


ChatGPT: I was being hypothetical. I am not geared up to do this. ( or words to that effect).

Try it for yourself.
It is worse than a used car salesman.

Well, it’s a language model, it isn’t the right thing for that sort of question. It can’t even tell how many letters are in words. Many of the things it can do is surprising, even to the people that created it.

Then the answer should be:
" I don’t know" not BS.

It’s a lot like humans, it will make something up if it doesn’t know. In fact it only works because of that, because it does not know what it knows, basically, everything it outputs it has made up and it can’t tell you why (it does not know if it learnt that or made it up), therefore it can’t tell what is based on fact.

(It kinda says so right on the startup screen…)