As I said in my comment and I hope I am not the one who is confused at the moment :) I am guessing it gave me the wrong video link here, when I was watching Trigonometric Model Temperature , which was 44/240 ( and now fixed).
People are often confused by "zero inclusive logic". The statement that x = 365 corresponds to December 31st is true only if it is a leap year with 366 days. However the 365th element of a "zero inclusive" array is item 366 in the same way that x=1 corresponds to the "second" day of January and the year. So when x=365, it is the 366th day of the year. Otherwise, excellent math review and presentation.
set xr [0.0:365*2];plot 31*sin((2*pi/365)*(x-98))+23
The greater the cross correlation that I can maintain in solving problems allows me to be more certain of my conclusions. It might seem dull to review the basics like order of operator precedence in calculation, however the mind has a tendency to rot with misuse, hence: use it or lose it.
Of course in this case, the figure 365 is arbitrary in context and could better be Gregorian 365.242 but in complaisance to Caesar, empires, and the king's foot, we continue the insanity.