credit card fee realization...

So, Do you know how your credit card fee is calculated? I just figured it out!

We've been watching our credit closely and learning how to raise our credit scores (without paying lots of interest fees).
We bought a couch last week and I wondered how the credit cards come up with the seemingly random finance-charge so I found out something very interesting.
They charge a tiny interest daily (.04%) SO I wanted to know how much money we would be paying if we put the couch on credit for 1 month verses 1 day.
In other words: what would we save by paying the charge the day after the charge instead of at the end of the month.
TAKE A LOOK!...
$18.75 vs 63cents !