function out = c2(sd2)

global sn;
global alphaP;

s2 = sn .* ((4.*sqrt(pi/3).*sd2.^3).^-1);
out = sqrt(2) .* s2 .* (erfinv(1-alphaP));

% Best guess threshold, since their's doesn't
% seem to be stable in this case . . . .
%out = (6 * sn) ./ sd2.^3;

