Extech DO600 Waterproof ExStik II Dissolved Oxygen Meter

Ideal for Rivers Trust Organisations to find out what are the oxygen levels in slow overgrown watercourses resulting fromm poor EA maintenance and abrogation of statutory duty.. In Durable case

Avoid buying these or using this manufacturer.I was hoping to use the device in field and lab settings to determine the dissolved oxygen content of water samples.I also have a Jenway and an older device which still work, but for teaching purposes we needed several and Extech looked like a great alternative so I purchased three. While, the existing Jenway devices and one of my Extech DO600 Waterproof ExStik II provide measurements that agree with one another, two of the Extech DO600 Waterproof ExStik II devices provide readings that are completely impossible.The devices were calibrated in exactly the same way as each other. I raised the issue with the sales team at Extech because they do not provide any customer service contact details but I could find a sales email address online (unsurprisingly). Nobody has answered my query, so presumably they are happy to sell the devices, which do not work, and they prefer not to hear from customers and do not intend to deal with faulty items.It's very disappointing as we have a limited budget and this has cut into it as we'll need to source alternative devices without receiving any refund, or even any suggestions as to the source of the fault/troubleshooting.