As I am just sitting over "The Normal Distribution", I wonder whether there might be a mistake in my guide, probably copy-and-pastish or so.
On page 91, Gd. 5, the 2/3 example for the normal distribution explains:
Roughly 2/3 of the example will fall within 1 standard deviation of the mean. Thus in the above example, a value of 6 is at roughly 50% - 50% - (1/2)(2/3) = 17% ≈ 17%, or the 17th Percentile. A value of 14 is at roughly 50% + 50% - (1/2)(2/3) = 17% = 83%, or the 83rd Percentile.
Well, I am sitting in front of my desk and I simply don't catch it as it is written. However, 50% - (1/2)(2/3) = 17% and 50% + (1/2)(2/3) = 83% would make sense.