How ordinate measuring the pros and cons
ordinate measuring how negative and positive
are you asking why some values are negative? In the example you have given the you have specified ordinate dimensions to the left and right of the 0 location. This is why some are positive and some negative. If the 0 location was specified at the left hand edge all dimensions would be positive. In ordinate dimensioning you basically specify a dimensional origin and all subsequent ordinate dimensions are related to that.
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