set term qt font 'serif,14'

a=0
b=0

fit a+b*x 'cv8/upf_cv8_extrap.dat' via a,b

set arrow from 14, -20 to 14, 10 nohead ls 0

plot [0:15] 'cv8/upf_cv8_extrap.dat', a+b*x

# precteno z textoveho vystupu gnuplotu:
sigma_a =  0.5336
sigma_b =  0.086
cor     = -0.886

#sigma(x) = sqrt(sigma_a**2 + (x*sigma_b)**2 + 2*x*sigma_a*sigma_b*cor)

#replot a+b*x-sigma(x) ls 3 t "", a+b*x+sigma(x) ls 3 t "1 {/Symbol s} band"