Goofy Units of Measurment in the Sciences: Tap Density

Tap density is used to describe different types of metallic powders. Below is a description of a $35.00 article on tap density from the American National Standards Institute:

The principle of the method specified is tapping a specified amount of powder in a container by means of a tapping apparatus until no further decrease in the volume of the powder takes place. The mass of the powder divided by its volume after the test gives its tap density. By agreement, the tapping may be carried out by hand.

For about five weeks, I've been under the assumption that my boss had been refering to "tab density." In some ways, I wish I had never found out the truth. [Link]