Instructions
Begin a new game of Counter-Strike. Go into the "Options" menu. Select the "Game Settings Tab" and check the box enabling the console window.
Exit the options menu and press the ~ (tilde) key. This will bring up the console window. Once in the console window, type "net_graph 1" and "net_graphpos 2" (without the quotation marks). The FPS will display.
Type "net_graph 1" and "net_graphpos 2" (without qoutation marks) in the console window. The FPS will display. As an alternative to typing the above commands, type "cl_showfps 1" in the console window without quoutation marks. Another FPS reading will display.