Find out about current 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.
A numerically lower order generally implies a more reliable height.
|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 ±2mm√k, where k is the distance in kilometres.|
|2||Third order spirit-levelling with a maximum closure error of ±7mm√k, 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.|