Fingers

From TheAlcopedia

A slightly-less-than-official measuring unit for drinking games. Open to much debate and cheating- basically 1 finger of your drink is achived by putting your finger on the glass where the level of the drink is next to the top of your finger. Then, lifting your glass and keeping your fingers FIRMLY IN PLACE you drink until the level of the drink is at the bottom of your fingers.

To do this for more than 1 finger unit, just place the other fingers below the first one. Simple!