YSI 55 - Manual (Page 13)

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5. When the proper altitude appears on the LCD, press the ENTER key. The Model 55 should
now display CAL in the lower left of the display, the calibration value should be displayed in
the lower right of the display and the current DO reading (before calibration) should be on the
main display.
6. Make sure that the DO reading (large display) is stable, then press the ENTER button. The
LCD will prompt you to enter the approximate salinity of the water you are about to analyze.
You can enter any number from 0 to 40 parts per thousand (PPT) of salinity. Use the arrow keys
to increase or decrease the salinity setting. When the correct salinity appears on the LCD (zero
for fresh water), press the ENTER key. The instrument will return to normal operation.
Once the calibration process is complete, the only keys which will remain operational are the
MODE key, the LIGHT key and the ON/OFF key. You can move back and forth from reading
dissolved oxygen in the mg/L mode or the % air saturation mode by pressing the MODE key. If you
are working in a dark area and have difficulty reading the LCD, press and hold the LIGHT key to
activate the back-light of the YSI Model 55. The ON/OFF key turns the instrument on or off.
For best results:
• Each time the Model 55 is turned off, re-calibrate before taking measurements.
• Calibrate at a temperature within ±10°C of the sample temperature.