QA Bulletin from February 2006, Calibration of Dissolved Oxygen Meters

If dissolved oxygen is a critical parameter, EPA New England recommends a second calibration point using the zero DO solution or a check of low DO accuracy with a zero DO solution.

• QA Bulletin: Calibration of Dissolved Oxygen Meters: February 2006 (pdf)
  If dissolved oxygen is a critical parameter, EPA New England recommends a second calibration point using the zero DO solution or a check of low DO accuracy with a zero DO solution.