Maximum Comfortminder - Manual (Page 2)

stated earlier, it is to be used in areas of persistent low relative humidities. If
COMFORTMINDER is subjected to such conditions, periodically follow initial
activation instructions. This procedure does not apply to nor will it affect the
temperature portion of COMFORTMINDER.
* COMFORTMINDER is measuring the relative humidity and temperature at the
location of the indicator, not at the local weather forecasting station. Relative
humidity and temperature, like many other elements, can be drastically different
with the smallest change of location.
* Your COMFORTMINDER case is jewelry quality brass with a durable finish. Do
Not clean with abrasives.
* Attempts to alter calibration will only destroy the elements and void your 5-year
warranty.
Because humidity is the least understood and most difficult function of our environment to measure accurately,
the following essay should be carefully read to help you use and understand your COMFORTMINDER.
UNDERSTANDING HUMIDITY MEASUREMENT
A commonly asked question is, “why does my COMFORTMINDER read a different humidity than the weather
service, or another hygrometer in my home?” To adequately answer this question we must first explain a little
about humidity measurement.
Humidity is defined as the amount of water vapor present in the atmosphere. The simplest way of expressing
humidity is as the absolute humidity. Absolute humidity is the density of water vapor, or the mass of the vapor
divided by the volume. The problem with this form of measurement is that it can vary as much as five orders of
magnitude (i.e. 1 to 100,000) over the surface of the earth at any point in time. Because of this large variation,
absolute humidity is not a useful form of measurement to most people.
A number of other measurements of humidity have been defined to correlate natural phenomenon with humidity.
Specific humidity is the ratio of the mass of water vapor to the mass of natural air. This form of measurement is
useful because it has less variation and is independent of temperature and barometric pressure (altitude). Specific
humidity is often used to relate the different forms of humidity measurement.
Relative humidity is by far the most popular form of humidity measurement. By definition, relative humidity is
the ratio of the measured vapor pressure to the maximum possible vapor pressure at the measured temperature. In
simpler terms, if the relative humidity is 50% then the air is holding 50% of the maximum amount of water vapor
possible at that temperature. Relative humidity is the measurement of humidity that most closely relates to
natural phenomenon. Some examples are, the changes in organic substances (i.e., the shrinking and swelling of
wood), the performance of electronic devices, and the level of comfort that we feel.
It was stated previously that specific humidity is independent of temperature and pressure. Relative humidity,
however, is dependent on temperature and pressure. Therefore, the relationship between specific and relative
humidities is governed by temperature and pressure. In general, barometric pressure doesn’t vary over small
areas. Also, of the two variables, pressure and temperature can vary greatly in a small area. Therefore, we will
only consider the effect of temperature on the specific versus relative humidity relationship.
You can convert one version of humidity measurement to another by using complex mathematical formulae, a
table or a chart. A typical chart, known as a psychrometric chart, relates all of the basic humidity measurements.
We have included a simplified chart to facilitate comparison of specific and relative humidities.
Generally, the specific humidity in a small area (i.e., inside a building or around a yard) is constant. This is due to
the fact that most substances in the atmosphere (i.e., smoke, water vapor) tend to disperse evenly throughout the
air mass by a process called diffusion. Additionally, the specific humidity tends to be fairly constant from outside