Good find ie. L.Motus & M.G.Rodd in their book "Timing Analysis of real-time saftware" pretty much categorise the "real world" as a part of the program/computer system or more precicely a computer system as a part of the bigger "program" the real-world.
Understanding the errors and lags on instrumentation is important also.
PS. thx danw I also look that book, might be interesting. +1
You beat me to it. Tony's book is a great way to go. I can also help provide a ton of data, but I would need to know what kind of stuff are you looking for specifically.