According to cartometric scholars, the early normal portolan chart typically used three differing map scales - one for the Atlantic region, another for the Mediterranean Sea, and a third for the Black Sea, with the result that the distances in the Atlantic were understated and in the Black Sea relatively exaggerated.^[24]. This might be an error interpreting data, or deliberate (as the Black Sea was frequently sailed by merchants, and needed to be "zoomed" in for detail). Portolan charts usually have a small distance scale drawn somewhere on the map - usually a small bar with spaced lines and dots. However, this scale is usually unlabelled and its correspondence to actual distance measures (leagues, miles, etc.) left unspecified.^[25] The scale bar drawn in a normal portolan seems to correspond best with the Mediterranean scale.

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