The book, and Tufte, focuses on effectively displaying quantitative information. He takes a relatively hard line about it and I have found it one of the most useful texts for helping me take "some truth the system knows" to "some truth the user knows".
Of course you have to take it with a few pinches of salt.
Firstly it is largely his opinion. Studies into this area are rather good on the general points however the fine detail is incredibly hard to study accurately.
Secondly you may not actually want to make a UI that conveys the "truth it knows" above all else. Often you want to convince the user that the UI is good at conveying information (which is not the same thing) or that it is very easy to use (which is again, not the same thing).
I heartily recommend this book because it teaches one very hard thing very well. You just have to understand that you do not always want to do this thing (yet you now have a way to start to understand the trade-offs you are making).
There are two more books, on concepts I believe, and verbs.
It's not the most practical way to learn UI design, but I enjoy how well it makes the case for good UI. Too often, I see programmers dismiss design. It seems not to fit into their scheme of values, i. e. "it's not scientific" or "it's just shiny packaging " or "it's something for beginners – I'm an expert". Then you get some guy replace all custom fonts on npmjs.com wit Arial because "all sans-serifs look the same anyway".
(the example is more "design" than "user interface" but it's the best one I remember)
One of Tufte's main themes was, I thought, that only information that directly conveys meaning should be included, and everything else should be thrown out. Where everything else, in the context of UI design, would probably be excess styling. On the other hand, I forget where I read it but we know that people are biased into finding more attractive interfaces more usable, even if a "usability expert" might disagree. So personally, I find Tufte's title fitting - he really is talking about effectively displaying quantitative information.
The book, and Tufte, focuses on effectively displaying quantitative information. He takes a relatively hard line about it and I have found it one of the most useful texts for helping me take "some truth the system knows" to "some truth the user knows".
Of course you have to take it with a few pinches of salt.
Firstly it is largely his opinion. Studies into this area are rather good on the general points however the fine detail is incredibly hard to study accurately.
Secondly you may not actually want to make a UI that conveys the "truth it knows" above all else. Often you want to convince the user that the UI is good at conveying information (which is not the same thing) or that it is very easy to use (which is again, not the same thing).
I heartily recommend this book because it teaches one very hard thing very well. You just have to understand that you do not always want to do this thing (yet you now have a way to start to understand the trade-offs you are making).