Ln differenced price level times 400, why 400? I am replicating a 2001 Journal of Economic Perspectives methodology paper on Vector Autoregression by James H. Stock and Adam Watson. The paper can be found here: http://faculty.washington.edu/ezivot/econ584/stck_watson_var.pdf

I'm having a slight problem with the log differencing. In the paper the researchers state that they multiply the ln differenced price levels by 400. 

I have no clue why this is done. The price level data is quarterly chain-weighted and seasonally adjusted implicit GDP deflator of the US. I would understand if they would multiply by four to get the annual inflation figures, but this is unclear. Any suggestions?
You already accounted for multiplication by 4. Further multiplication by 100 to make the units of measurement percentage points? I.e. inflation is usually referred to as 3%, not as 0.03.