linear and polynomial: the coefficients from x⁰ up, [c0, c1, …];exponential: [a, b] of y = a·e^(b·x);logarithmic: [a, b] of y = a·ln(x) + b;power: [a, b] of y = a·x^b.x is the series' x on a scatter, else the category's number from 1.
Excel's R²: the square of the correlation between the series' y and the fit's.
A fitted trendline's numbers.