Normal-Orthometric Height Orders

Normal-orthometric heights in terms of the 13 mean sea level vertical datums are classified into five orders according to the way that they were observed.

The following table lists the vertical orders used with normal-orthometric heights in New Zealand. A numerically lower order generally implies a more reliable height.

Order	Description
1	First and second order precise levelling carried out to full precise level specifications on stations constructed to acceptable benchmark standards. The maximum closure error is , where k is the distance in kilometres.
2	Third order spirit-levelling with a maximum closure error of , where k is the distance in kilometres; precise levelling of marks not constructed to acceptable bench mark standards; simultaneous reciprocal trigonometric levelling over short lines provided origin has a 1st or 2nd order height.
3	Less accurate levelling than above provided the origin has a 1st, 2nd or 3rd order height; systematically adjusted trigonometric levelling with good adjustment corrections and reliable fixed heights.
4	Conventional systematically adjusted trigonometric levelling with poor adjustment corrections, weak fixes, long lines or hanging line connection.
5	Station height of unknown reliability or doubtful accuracy.

A mark may have coordinates in multiple geodetic and vertical datums with different Orders in each.