According to ASME Y14.5, a primary dimensioning datum requires at least 3 points of contact to establish the datum plane. Two points of contact are required for the secondary datum and 1 point of contact is required for the tertiary datum.

Datum is not the plural of data. Datum is singular, and its plural form is data.

Datum and gps

Correction: What is hydrographic datum? not "hydrography"

1. Question is really vague, it is important to mark out the selected datum, as you just selected that datum? What else are you going to do with It? If you are working from another datum point just ensure that it is a good datum with critical measurements checked otherwise the new datum could throw out al measurements.

P.s i wish the selected retards would stop answering with nonsense answers.