Many people in the internets love to cite Albert Einstein's quote about the compound interest. Interestingly, right upon citing that, many of the same people pour their hard-earned pennies into some scammy looking HYIP projects. Personally, I don't remember Einstein talking about HYIP projects. Actually, I don't remember Einstein talking about compound interest either. Maybe because I simply haven't read much of Einstein and have understood even less.
Anyway, mathematically the compound interest is a proven theory. That is, it does work as promised, Albert Einstein could guarantee you that.
And quite by chance, I know a tiny BTC faucet that could illustrate various aspects, both arithmetical and not, of compound interest, hassle-free.
Here it is
To sign up you will need a login, password, and a BTC address. Upon signing up you will see an ordinary BTC faucet with 3 sats every 15 minutes. Not very impressive. What is impressive is a "generator", i.e. an interest-bearing account with 3500 sats on it as a welcome bonus. This generator generates 1 sat per hour, which can be reinvested back into the generator. That's all, no deposits, captchas, banners or fees.
(the balance on the screenshot is more that 3500 sats because I've already put a bit in)
It works very simply -- sign in once a day (or every 10 hours, if you wish) and push the "Invest" button. You may also claim satoshis, watch banners, do CPU mining, but normally it's not necessary.
I'd call this faucet "a free practical education on compound interest theory". E.g. you could do the math and calculate when it will reach 0.00055 btc of daily payouts (that's the min withdrawal amount). Doing the math you'd consider additional variables, such as typical HYIP's life trajectory or Calvin Coolidge's word on persistence.
Disclaimer: I'm not an employee or owner of any crypto-exchanges or faucets, including the above-mentioned one. This article is informational and not financial advice, endorsement or a guarantee of any kind.