girl, that's it. There are some decimals in multiplication that give an extra margin, lol, math is all right, if it's less, it's a fee that you paid using the currency and you don't know how much it is in dollars.

If you buy 1000 reais of BTC when the price is $ 105.000 and that value drops to $ 104.000, your 1000 will decrease (obviously) but then the value of BTC returns to $ 105.000, your balance does not return to 1000 reais lol.