Manually Zeroing G7Using the up and down buttons, scroll through the menu and select Gas Options by pressing the OK button. By default, G7 zeroes all sensors. Press the OK button to display the Gas info menu. Important: If you see a zero incomplete message on your screen you may be in an environment with gas levels, or your cartridge may need to be replaced. Contact your organization's safety professional or the Blackline Safety's Technical Support team for assistance troubleshooting your device.