help with Alliant Load Data?

[eschafer]

Found this chart of load data from Alliant (see below)... Can someone enlighten me what the dimensions listed in the "notes" reflect? I assume "C" means "compressed". "air" means not compressed? But what are the dimensions in inches for? I know it's likely obvious, but today I'm too thick to figure it out.. Thanks...

https://www.alliantpowder.com/downloads/RL16_Initial_Loads.pdf

 

[Ned Ludd]

Presumably, those values are in relation to the height of the powder column...i.e. a certain distance "compressed", or a certain distance of clearance or air space above the powder column to the base of the bullet. I have no idea why a reloading manual would list such distances, they have little meaning as they have no way of knowing how well you packed the powder into the case (i.e. using a long drop tube or vibratory means to obtain better packing). Using the term "compressed" or not should be sufficient.