The callout is a common engineering standard that sets "medium" general tolerances for a part's size and geometry. Instead of labeling every single dimension with a plus-minus value, adding "ISO 2768-mH" to your drawing's title block establishes a global default for all untoleranced features.
You don't have to clutter your CAD exports with "±" values for every single fillet or shoulder. iso 2768-mh tolerance chart
class tolerance for geometric features like straightness, flatness, and perpendicularity. ISO 2768-1: Linear Dimensions (Medium Class "m") ISO 2768-mH The callout is a common engineering