why is there a dancing ad on the side of my calculator?

Because...,that we can have fun with maths -- free  of charge!

Thanks, Admin !

Because this is a commercial site.

No one inside this forum gets paid a cent (nor does anyone get charged anything)  but the owner of the site has spent an enormous amount of time creating the calulator and the site in general.  Plus he has a lot of running costs.  All this must be paid for.  The advertising recovers some of these costs for him.  He has kept the advertising quite unobtrusive which is very nice of him.    

i did not know that, Melody

on my PC, I don't see any ads ever

That is really cute, thanks Civonamzuk  :))

HeatherF, the ads change all the time.  Sometimes there isn't any :))

NO ad now!