Singapore legislation
Regulation 18
of Boundaries and Survey Maps (Conduct of Cadastral Surveys) Rules 2005
Regulation 18
Datum
Subregulation 1
A registered surveyor must traverse and connect at least 4 ISN markers to establish a datum acceptable to the Chief Surveyor for every survey of a land lot.
Subregulation 2
The ISN markers must fully enclose the survey area, unless the Chief Surveyor directs otherwise.