GNUPLOT- how to change the style of data points

Hi,

I am trying to arrange my graphs with GNUPLOT. Although it looked like simple at the beginning, I could not figure out an answer for the following: I want to change the style of my data points (not the line, just exact data points) The terminal assigns first + and then x to them but what I need is -, _ or simple dots (.). Does anyone know how to do that? Thanks,

Natasha