function gco_plotter(Tgco, Tgco_air)
global Tk
n = length(Tgco);
z = 0:1/(n-1):1;
z = z';
T1 = Tgco-Tk;
if length(Tgco_air)==1
  T2 = Tgco_air*ones(n, 1)-Tk;
elseif length(Tgco_air)==length(Tgco)
  T2 = Tgco_air-Tk;
end
figure
plot(z, T1, '--', z, T2, 'k')
xlabel('Position $\brunit{-}$')
ylabel('Temperature $\brunit{\dcu}$')
text(0.6, 60, 'legend')
