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    David Velasco

    Hi Leonard

    Thanks for reaching out to us, and thanks for sending the photos.  Looking at the photos I do have some comments.

    First, the Eco's frame is Delrin (not aluminum) and obviously cinder blocks and sand are non-magnetic. But, you have quite a bit of metal chain around the tripod and, while the photos do not show, it's likely they are magnetic. It's hard to say if they impacted the measurements or not (you'd have to duplicate the exact setup with/without all that chain to confirm), but that would be an obvious place to check.

    Second, while cinder blocks and sand are easy to come by, they make for bad anchors. Their submerged weight is significant less than their air weight, with concrete losing almost half of its weight underwater. Non-magnetic metals such as lead are MUCH better. In the Eco App, please review the FAQ "What should I use for anchor weight when using the Eco buoys?" for a handy table, as well as the Video FAQ "How to use the bottom frame?" for an example of good anchors for the Eco tripod. 5 lb dive belt lead weights on each leg will hold the frame in about 50-70 cm/s water without a problem. For your site, where you are getting up to about 1 m/s, doubling that should suffice and will make your installation a lot smoother and easier :-)

    Looking at the data itself, I'm not seeing any indications that something is wrong, so the directions, while might not match your expectations, may very well be accurate for the exact spot your Eco was deployed (flows can be dynamic in shallow areas). However, if you'd like to verify your Eco's compass just as a sanity check, you can do a short in-air test, with a short Measurement Interval, while having the Eco pointing to magnetic north (the little notch on the side of the head, next to the pressure port, is the Eco’s -X direction and from there it follows a right-hand coordinate rule). Let it run for a few Measurement Intervals, then rotate it clockwise by, say, 90°, then let it collect a few more Measurement Intervals, then repeat the process until you've gone full circle. Of course, you'll need to do this outside and away from any magnetic interferences and buildings.

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    Leonard Barrera Allen

    Thank you David for the clarifications, and well noted on the anchors weights - will save a lot of time for our next deployments.

    You mentioned you looked at the data. There are some gaps in the velocity data measurement period. Is it correct to assume these gaps are there because the measurements did not meet the automatic quality control checks in the post-processing? Is it possible to look at this data?

    Thanks again!

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    David Velasco

    The short answer is yes, these measurements did not meet the automatic QA/QC and are therefore invalid.  As a rule of thumb, for the Eco, if data is present, they are valid.  If absent, then they are invalid.  Given that they occurred at the time of maximum velocities and are followed by a noticeable change in tilt, and it recovered later after the currents slowed down, it's likely we're looking at some type of temporary beam blockage here.  Which is also another downside of large anchor weights: their size can increase the amount of erosion and sediment movement around the frame, which wouldn't be observed if the frame was more streamlined.  

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