Galvanic Timed Releases, GTR's or Pop-ups are devices that essentially dissolve at a known rate in sea water. 

Researches use them to release testing equipment from equipment or sea creatures.  

In the image below, the hash mark on the left edge of each block represents the actual release time at the temperature range above the chart.  Each block has a 6 or 12 hour burn loss.  If the Pop Up release timing is longer than desired, the Pop Up can be 'burned off' by pre-soaking them in salt water to corrode off the extra hours.

10 pcs per pack

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