Today in 2007, US Patent 7255003 B2 was issued, an invention of Calvin R. Schneiter, for his “Device For Measuring and Displaying the Amount of Beer in a Keg.” Here’s the Abstract:

A scale for determining a quantity of material in a container such as a keg. The scale may include a support member configured to be placed under a portion of the container, a display to indicate the quantity of material in the container, and a weight sensor positioned underneath the support member to determine the quantity of material in the container and to provide a signal to the display.