Carried by government weather bureau or similar official agency.

Quantity limits: N/A

May only be carried by a representative of a government weather bureau or similar agency.

Must be in carry-on baggage only.

The individual must advise the airline of the presence of the mercury barometer or thermometer in the carry-on baggage.

Must be inside a strong outer packaging having a sealed inner liner or bag constructed of strong, leak-proof and puncture-resistant material that is impervious to mercury and will prevent the escape of mercury from the package in any position.

See the regulation: 49 CFR 175.10(a)(13)