Perimeter of the Ellipse (HP-15C)

[Albert Chan]

(06-05-2021 08:00 PM)Gerson W. Barbosa Wrote:  A better option for both 10 and 12-digit results is to discard even the 1/3 constant:

p(a, b) ~ π(a - b)(y + 1/(4y - 1/(4y - 3/(4y - 3/(4y - 11/(12y - (4/(2y - 1))))))))

Try replacing last constant 1 as (19/18)/y.
This keep rel error below 1 ppm, well until h = ((a-b)/(a+b))^2 > 0.9616