Chapter 3 Datums 117 8X ∅5.85 (6.0-.15) MMB Datum feature simulator of datum feature B Datum feature simulator of datum feature A fixed at basic Datum feature A must remain in contact with the simulated datum feature 10 The Drawing Basic All around Origin of mathematically defined data The Meaning Example 3-44. Establishing a contoured surface and a mathematically defi ned feature as a datum feature.