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I see what you mean on their product page: “When used with the ZL6 data logger, you won’t require an additional sensor for measuring—and referencing—barometric pressure.”
However, both the sensor manual and the Integrator Guide in the Downloads section describe the vent for atmospheric correction, as expected — definitely an inconsistency.
FWIW, my most recent HYDROS 21 purchase was March 18th, and it’s got the vent. The part description on the Meter invoice says “40683-S CTD-10 (HYDROS 21) Sensor, Stereo end, 10 meters”. It’s got the new black cable, but I don’t know whether that indicates it’s a gen 2; the website only appears to mention gen 1. The only other change I can see visually is that the hook on the mesh Kellem cord grip could be more easily removed because it’s held on with a threaded link, rather than being clamped directly to the grip.
-Matt
