Read the following technical passage and complete the statement based strictly on the text:
Aviation maintenance technicians service high-pressure aircraft tires using dry nitrogen gas rather than standard compressed air. Nitrogen is preferred because it contains virtually no moisture, preventing internal corrosion of the wheel assembly and reducing rim degradation. Furthermore, unlike oxygen, pure nitrogen does not sustain combustion, which minimizes the risk of tire explosions during extreme braking temperatures upon landing. The operational manual requires tire inflation pressures to be measured exclusively with a calibrated digital gauge while the tire assembly is cold.
What specific instrument does the operational manual require technicians to use when checking tire inflation pressure?