Based on in-depth testing with the Ultima X Gas Monitor, MSA has changed the calibration recommendation for HF Sensors:

• All HF sensors leaving the MSA factory are now calibrated using SO₂ with a span setting of 8.0 ppm.
• The flow rate used for calibration is 0.25 lpm and the SO₂ cylinder is P/N 10028070.
• For older sensors already installed in the field, it is recommended that the span setting be changed to 8.0 ppm and an iCal performed with SO₂.
• This update can be accomplished by using the Ultima Controller.
• Although the old HCL calibration is acceptable, the new recommendation provides greater stability over temperature and humidity ranges.