Just a FYI. I don't know about the other meters, but the YSI requires that the probe be continually moved back and forth or up and down to continually have new water flowing over the O2 membrane to get a good reading. If you let it sit in one spot, the O2 reading keeps dropping. The sensor is stored in a chamber on the unit that has to stay moist or the membrane will dry out and become useless. A replacement membrane kit is around $50 and you get 6 replacements.
I marked the cable in 1' increments with electrical tape to have an accurate way to measure how deep the probe is.
They are all pretty much the same unless you get into the high dollar optical units.
I just read the manual on my Extech unit and it requires a velocity of 0.6 to 1.0 FEET per Minuit to get an accurate reading. Also the membranes last a long time. You fill the end of the sensor with KCL solution and it keeps everything nice and wet. There are no other requirements except to rinse it off, preferably with distilled water when you are done. The Mettler Toledo sensors I have are similar, but are industrially hardened stainless steel units and will work accurately in static conditions.
One thing neat to do with a unit that measures Atmospheric O2 levels, is to take it with you on your daily routine. The closer you get to a city, or in traffic, you will see a big drop in O2. Then go out to the forest, or farm country with vegetation, and the O2 levels really get up there.
My bad Cecil, YSI is made in the US. Sorry about that.
FFF, I think it would be bad policy to sell something to a forum member. That is just not a good idea in my book. As soon as it warms up a bit I will take inventory and put a bunch of stuff on CL. "Epay through your nose" charges sellers too much to sell. Then "PayME More" adds another 3%, even on the shipping.
