I found out about medical calculators, used for lives-are-at-stake calculations like drug dosages. If I haul out my phone calculator and type in 2 3 · 4 , it ignores the second dot and shows 2.34. But it's strange that I hit the · key twice—one of those was probably an accident. Maybe I meant to enter 2.34, maybe I meant 23.4. These fancy-pants medical calculators are more careful: they show a warning about the too-many-dots problem. (The book also discusses a problem that can arise from using too many fancy-pants complex error checkers: if the system gets too complex, that's just more opportunities for errors as layers of a system interfere with each other.)
I found out that the Spurious Correlations website is pretty funny and reminds us that plenty of unrelated things correlate with crime rates, cancer rates, whatever rates; and you should take any pundit's discovery of the true cause of whatever with a big grain of salt. I found out about a project Tommy Flowers worked on after his WWII codebreaking work: ERNIE, a random number generator that generated entropy from neon tubes. I learned… uhm, there's a lot of cool stuff in this book. Recommended; check it out.