tone function

I downloaded some code for music and the programmer used the tone and delay functions in a way I never saw. Example:

tone(tonePin, 523, 1499.21875);
delay(1665.79861111);
delay(0.868055555556);

I isolated each of the lines of code and each tone plays a specific note, but I don't understand the code and why they used such strange numbers. Can anyone shed some light on this?

Where did you find that code? Instructables? The delay() function and the tone() function take unsigned long integers. Any float passed as a parameter to either function will just be rounded down so

delay(1665.79861111);

will be 1665 and

 delay(0.868055555556);

will be 0.