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| SECCHI DISK |
| The secchi disk measures light penetration below water. By using this secchi disk you can limit the visibility of the light transmission. If you are in a clear ocean the secchi disk can measure light for up to 40 meters or more. |
| It is seen. |
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| Still seen. |
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| Bareley see it. |
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| Now you can not see it. |
| This is how the secchi disk goes underwater. |