YSI 556 MPS - Manual (Page 95)

System Setup Section 10
YSI Incorporated YSI 556 MPS Page 89
6. Use the keypad to input the known barometric pressure value
as determined in Step 2.
7. Press the Enter key. The new barometer reading is displayed
as well as the approximate offset from the factory reading.
NOTE: To return the sensor to the factory setting, subtract
the offset amount from the current setting and repeat Steps 5
to 7.
8. Press the Escape key repeatedly to return to the main menu
screen.