The "m" graph can be opened up by pressing the m key, hence the name the m graph. It monitors lag, how long you've been playing the match, and data. It appears over the radar on the top right of the screen. Lag is measured in ms (milliseconds) and is either negative or positive. If you have negative lag you are ahead of the server and it appears that your killing zombies when you are really not. If your lag is positive, your computer is behind the game but your kills will register. Explosive weapons will not cause splash damage if your lag is too heavy because by the time the zombies which it kills would die, they are in different places and your shot misses. If your lag number gets high enough, the game sometimes appears to freeze. In some cases, your game will unfreeze, but it is far more common for frozen games to be completely unwinnable and waste your ammo. One glitch that often occurs in frozen games causes weapons to fire at many times their normal rate, wasting ammo immensely. If this occurs, your only options are to switch to pistol and hope your game will unfreeze or to hit spacebar (pause/equip menu) and quit the game. The line data Tx is data being transferred out of your computer and data Rx indicates data being received. The total is, as you can see, the sum of the two.