I'm interested in something somewhat different. So from the Keynesian perspective statements like "an income based measure of output and an expenditure based measure of output should be equal" needs a little more elaboration, because the Keynesian point is precisely that it's the process that makes these two equal that is so essential to understanding the business cycle.
So what is a business cycle? The most fundamental description is that it's when expenditure is "trying to be lower" than income, and income is adjusting dynamically. There are a couple different processes to look at when we talk about the dynamic adjustment: (1.) consumption behavior and the multiplier, (2.) money demand, interest rates and investment demand, etc. But that's the story in a nutshell.
UPDATE: I read the graph wrong - read the comments below for details and for some thoughts on what is going on. Bob Murphy talks about it here too. Any other ideas?
Which brings us to figure four in the Nailewaik paper (page 88). Now that is a fantastic graphic: