The Frenchman Island sea-level recorder pictured below. is a pneumatic gauge (also known as a bubbler). For details of how a bubbler works click here.

The Frenchman Island sea-level recorder samples at 1-minute intervals. Every hour it sends its data by radio to the NIWA office at Bream Bay, where the data are transferred into the Internet by ftp (file transfer protocol). A few minutes later the data are downloaded in Mulgor's office in Christchurch where they are processed, converted into information, and uploaded back to this page on the Internet.

Frenchman Island with the sea-level recorder atop.
The concrete structure near water's edge is an old acetylene gas holder, a relic from when the island was used as a lighthouse.
The bubbler's gasline comes through the scrub, past the concrete structure and down into the water to about 1 m below Lowest Astronomical Tide.