This is a template attribute. Template attributes can be used in filtering, or to retrieve data from the model to use in drawings and reports. For example, when you create a report, Tekla Structures replaces the attributes added in the report template with the corresponding object property values.

Shows the distance from the part surface to the reinforcing bar, perpendicular to the bar plane.

This is the first value entered in the From plane box in the Single rebar or Rebar group properties.