Just fwiw, I have never heard the expression "comparing chalk and cheese", used in the way I have heard "comparing apples and oranges." The most common use of C&C up here in Zild is in comparing people - "those two are like chalk and cheese". The meaning is closer to "oil and water", or at least conveys an odd pairing. No doubt Pfranz will correct me, but we do the use the phrases "comparing apples with apples" and "apples with oranges" for use hen describing comparisons of things. To my ear, the Zild use of C&C has more to with compatibility than comparability. Just my $0.02