A short book, a quick read, and a nifty historical document capturing an earlier, freer-wheeling age of C programming. There's some nice detail here about calling conventions, optimizations, efficiency, and library issues that you simply don't get from the "New Testament" (K&R 2nd ed.) and moreover, Plum is a lucid writer.
Be glad and grateful that the "entry" keyword did not survive the ANSI standardization process...