gnuplot how to make the grids solid lines

Question

I am just learning gnuplot and I want to plot a sensor signal with a grid, but no matter what I try the grid is always dotted and I want the grid to be solid line. I try setting linetype to -1 to no avail, can someone help me?

example

    set grid xtics lt -1 lw 1 lc rgb "#880000"
    set grid ytics lt -1 lw 1 lc rgb "#880000"
    plot [-10:10] sin(x),atan(x),cos(atan(x))

Answer 1

I just uninstall and reinstall GNUPLOT again and now is working.. no idea what was the problem, but that was the fix.

Thank you for all the help.