You might wonder why a millibar isn't exactly 1/1000th of an atmosphere. The unit is actually related to the old CGS units because atmospheric pressure is close to this unit. In CGS units 1 bar = 1000 dynes/cm2. Pressure is often incorrectly reported as kg/cm2, which is neither a legitimate pressure unit nor a standard SI unit (pressure is force/unit area, and kg are a mass unit, and SI units never mix kg and cm). So let's straighten out your friends on these units. Standard air pressure in this incorrect unit is 1.034 kg/cm2. The weight of a kg at the earth's surface is 980,000 dynes. So what is standard air pressure in millibars?
◦ 890 mb
◦ 750 mb
◦ 1013 mb
◦ 1143 mb