This is a brymen 257s logging voltage.
#!/usr/bin/env bash
echo 'Logging'
sigrok-cli --driver=brymen-bm25x:conn=/dev/ttyUSB0 --continuous -o /tmp/data.dat -O csv
trap "{ echo 'Quit...' ; exit 255; }" EXIT
Brymen plot script
set datafile separator ','
set yrange[8.980:9.010]
set autoscale x
set ylabel "Volts"
set xlabel "Samples"
set grid
bind "Escape" "unset output; exit gnuplot"
plot "< tail -n 50 /tmp/data.dat" using 2 smooth acsplines title "V"
pause 1
reread
Korad again with two y-axis
set datafile separator ','
set yrange[0.01:0.03]
set y2range[0:12]
set autoscale x
set ylabel "Ampere"
set y2label "Volts"
set ytics border nomirror
set y2tics border nomirror
set xlabel "Samples"
set grid
set key box lt -1 lw 1
bind "Escape" "unset output; exit gnuplot"
plot "< tail -n 50 /tmp/data.dat" using 3 smooth acsplines title "I" , '' using 2 with lines axes x1y2 title "V"
pause 1
reread