Don't waste your money! It doesn't really measure D.O. levels. It measures temps and what corresponding D.O. levels would be at saturation. (Notice how the numbers aren't flexible with the temp reading) You need to spend at least $200.00 for an actual D.O. meter and they get pricier than that.
I have a $750.00 YSI model and only use it for fish hauling. Why? Because in a recreational pond situation where you do not have fish densities has high as commerical growers, if you manage your pond correctly you shouldn't have to worry about D.O. problems. Furthermore if you have low D.O. it's proabably already too late. Do you have the equipment necessary to bring D.O. levels up quicly in an emergency anyway? Most recreational ponders do not.
Keep your pond at optimum levels of macrophytes, fish densities, and algae bloom and you shouldn't need an expensive D.O. meter. If you get ice and snow in the winter, if your pond had the right amount of deep water, and you aerate and/or keep the snow off the ice, you shouldn't have to worry about winter kill either. However, if you want to check D.O. anyway I would recommend one of these two as they are not as pricey as the rest:
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/732/cid/113 http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/747/cid/121 Whoops! Looks like the probe is sold separately on the YSI so the cost is more than listed for the meter. Just wanted you to be aware of that.
I have a friend that runs a trout hatchery and says he loves the Pin Point one. He says not only is it economical but it also does a good job.
