Keith.Williams. thanks a lot for the entire first part, it makes so much sense to me now. Just one little thing, can you rephrase the last paragraph.."It is this increased static pressure which causes altimeters to under read when the temperature is above ISA, and to over read when temperatures are below ISA"?
Because if you increase temperature, you say that density decreases but static pressure increases...and these are the two answers which it could be in the multiple choice question.
+++EDIT+++ Now this is confusing me even more...the actual total pressure is unchanged, so if static pressure decreases, dynamic pressure increases. Is the trick in the question being that the actual total pressure is unchanged?