YSI 550A Dissolved Oxygen Meter

When trying to calibrate the unit the word OVER or Undercomes on the screen,not sure how to fix the problem.I think the settings arenot set correct.Allthe buttons,and the backlight work accordingly .Unit is in good cosmetic condition.Selling as is.

The YSI 550A dissolved oxygen meter provides fast, accurate readings with simple, on-hand operation. Featuring a waterproof IP-67, impact-resistant case and innovative field-replaceable DO electrode modules, the YSI 550A Dissolved Oxygen Meter is a true field instrument capable of excelling in the most difficult applications.

The YSI 550A Dissolved Oxygen Meter measures both temperature and dissolved oxygen simultaneously using highly accurate thermistors and YSI\'s proven polarographic technology. The YSI 550A meter measures dissolved oxygen as both percent saturation (range: 0 to 500%) and mg/L (range: 0 to 50 mg/L). The accuracy of the YSI 550A is up to ±2% depending upon the range. Features of the 550A include: an easy-to-use backlit display, automatic push-button calibration, and a weighted, quick-sinking probe. The YSI 550A DO also has a built-in calibration chamber, low-battery indicator, direct salinity, and altitude compensation. Dissolved oxygen readings are automatically compensated for temperature.

Specs: by YSI

• Dissolved Oxygen (% Saturation)
  • Range: 0 to 500%
  • Accuracy: up to ±2% of reading
• Dissolved Oxygen (mg/L)
  • Range: 0 to 50 mg/L
  • Accuracy: up to ±0.3 mg/L or 2% of reading
• Temperature (°C or °F)
  • Range: -5 to +45°C
  • Accuracy: ±0.3°C
• Fast response times
• Meets IP-67 specifications
• Field-replaceable DO electrode modules