GIPS Dispersion/Standard Deviation requirements only, understand, additional, included

marsilni

This stuff is not clicking for me.  If I understand correctly, an internal dispersion measure must be shown of only portfolio’s that were included in composite the entire period (you get your choice of high low, interquartile, SD of equal weighted returns, asset weighted SD of annual returns).  Next:
5.A.2 (Schweser Book 5 page 208) requires:
a. three year annualized ex post standard deviation using monthly returns
b. an additional 3-year ex post risk measure if mgmt feels standard deviation is innapropriate
So what are a) and b) above?  Are they external measures?  Or are they the internal measures I mentioned above (in other words, does a. represent the internal dispresion using SD of equal weighted returns or asset weighted returns and b. represent the internal dispersion using high low or interquartile returns)?
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Further, in the problem on page 225, note 6 says “dispersion is measured as the standard deviation of monthly composite returns”, which is said to be wrong because it is an external measure.  How do you know it is external and what is the difference?