Signal is the latest book by Stephen Few covering data visualisation. Like all of the Few books I have read the focus is once again on leveraging the preattentive visual processing and inherent the ability of people to compare lengths, positions, hue and saturation to make understanding the data easier.
The biggest difference with signal to his previous work is his emphasis on statistical rigour in this book. He pays specific mentioned to making sure that the reader understands topics like random interaction effects (and viewing them with funnel charts), observing distribution patterns and shapes (highlighted with a number of different charts like frequency polygons, strip plots, quantile plots and distribution deviation graphs). In this volume he spends a significant amount of time looking at XmR charts and how they can be used for finding changes to the norm (actual signals) and highlights that these are the variations that should be examined.
Stephen Few continues to drive visualisation best practice as a core tenant for his works. Focusing his attention on best practice and deeper data storytelling. While reading this book I have already implemented one of the new visualisations taught to me (leveraging the work done by Jonathan Drummey) and have seen a number of places where other visualisations (like the XmR charts could be used. The trouble I see with these more complex charts is the understanding and explanation they require on an ongoing basis; this makes them difficult to implement for me as a consultant for an ongoing basis (I am unable to provide the ongoing support post deployment).
I think that signal is another great book by Few which is extremely useful to add to your collection. It also provides a number of good references for continued reading and is going to be something that I will refer back to again in the future.