Why am I not mining per day what the calculator said I would?
The calculator only provides you estimates according to the probability that you will win blocks with the capacity you entered. This estimate is over an infinite amount of time. So, basically, if all things stay the same, your average daily Burst will continue to get closer and closer to the estimate the longer you mine. However, all things don't stay the same, and the mining difficulty is constantly changing. This calculator is just to help you get an idea of what the mining returns could be, not what they will actually be.
Where is the currency conversion data taken from?
The BURST price and conversion to USD/EUR is taken from one of the exchanges, Poloniex.