I just bought a nice used dissolved oxygen meter and thought some others might be interested in getting one as well. I bought it from Randy Rushin of Water Monitoring Solutions 903-439-4741,
randy@water-monitor.com,
web page He sells or rents any kind of meter you could want, but right now he has one YSI-55 (digital) and four analog dissolved oxygen meters in used but good condition and for good prices.
I told him he ought to become a sponsor so I wouldn't have to resort to spam to get this info out there.

If you're in the market for a DO meter or just want to find out more, give him a call. He's good people and won't try to hardsell you. I bought my meter for
considerably less than the cost of a new one.
Hope this post is o.k., Bob. My quick check of the sponsors didn't reveal any that sold DO meters, so I thought this info would be helpful.