Линия тренда в gnupot

set output 'pic.jpeg'
set grid
set xdata time
set format x "%d/%m/%Y"
set timefmt "%Y-%m-%d %H:%M:%S"
set multiplot
set title "zagolovok1"
set size 1.0,0.4
set origin 0.0,0.1
set yrange [0:60]
set ylabel "y-axis" 
set xlabel "x-axis"
plot "SVK2017.txt" using 1:3 notitle with steps lt rgb 'red'
# "SVK2017.txt" using 1:4 notitle with steps lt rgb 'blue'
set title "zagolovok2"
set size 1.0,0.4
set origin 0.0,0.5
set yrange [0:60]
set ylabel "y-axis"
set xlabel "x-axis"
plot "SVK2017.txt" using 1:5 notitle with lines
#, "SVK2017.txt" using 1:6 notitle with lines
unset multiplot[br]