When targets are used for the primary datum, they must also be used for secondary and tertiary datums.

Primary Datum

The main reference point or plane used in dimensioning and tolerancing from which other measurements are based.

Secondary

Pertaining to an item or process that comes after the primary or main stage, often providing support or additional functionality.

Tertiary Datums

Reference points, lines, or surfaces on an object used in the hierarchical system of geometric dimensioning and tolerancing, serving as a secondary or third level of datum reference.