Every scientist at Black Mesa keeps a few tricks in the lab coat, and Half-Life is no different. Tucked behind Gordon Freeman's adventure is the developer console -- a command line that lets you tune your game, tweak your controls, and (in single player only) bend the laws of physics. Here is how to open it and put it to work.

Turning on the console. Start Half-Life, go to Options, choose Keyboard, click Advanced, and check Enable Developer Console. From then on, tap the tilde key (the ~ above Tab) at any time to drop the console down, and tap it again to close it. Type a command, press Enter, and you are off.

Handy multiplayer cvars. These settings are perfectly legal on the Zone -- they only affect your own machine and how the game feels to you:

• net_graph 1 -- shows a live readout of your frame rate, ping, and packet loss. Set it back to 0 to hide it. Priceless on a busy deathmatch server.
• fps_max 72 -- caps your frame rate. Keeping it steady can smooth out play on crossfire, boot_camp, or stalkyard.
• sensitivity 5 -- sets mouse speed. Lower it for careful crossbow work, raise it for close-quarters crowbar duels.
• cl_bob -- controls how much your weapon sways as you run. Dial it down if the motion distracts your aim.

The famous single-player codes. First type sv_cheats 1 to unlock them, then use:

• god -- invincibility. Headcrabs and HECU Marines cannot touch you.
• noclip -- walk through walls and fly across the map. Great for exploring Xen.
• notarget -- enemies ignore you until you fire.
• impulse 101 -- fills your HEV suit with every weapon and full ammo, from the Glock to the Gluon gun.

Keep Zone play fair. Those cheats are for single-player campaigns only. Zone servers run with cheats OFF, so god and impulse 101 simply will not work in a match -- and that is exactly how we like it. On the Zone, the only edge worth having is skill.

One last reminder: everyone in a game must run the same Half-Life version, right up through the final WON release. If a command is not behaving, grab the latest patch from the Downloads page and get back in the fight. Good hunting, Doctor Freeman.