With a far-inside globe, equilibrium time is 6 minutes, and using a thermocouple instead of a mercury thermometer the time is 10 minutes. In equilibrium the net heat exchange is zero. The faster the air moves over the globe thermometer the closer tg approaches ta. Our thermal sensations are not good indicators of surface temperature but rather we sense the rate of heat loss or gain e.g. in a thermally stable setting a tile floor will feel colder than a carpeted floor even though they have the same surface temperature because tile has a higher thermal conductivity than carpet. Surface temperatures can be measured by thermometers placed in direct contact with the surface of interest.
Surfaces can be a significant source of discomfort.
In S.I. units it is expressed in grams of water per cubic metre of air or space. On a normal day humidity remains fairly constant but it is relative humidity which changes considerably. Relative humidity is the ratio of the prevailing partial pressure of water vapor to the pressure of saturated water vapor at the prevailing temperature. This situation is very unusual inside buildings except at very cold surfaces e.g. breath on cold mirror. Dew Point is the temperature at which atmospheric water vapor starts to condense when the air is cooled - major problem for condensation in buildings.