Shades of science class! The Taylor 1330PJ Sling Psychrometer is a compact, streamlined instrument that measures the wet and dry bulb temperatures of the surrounding air and allows for immediate conversion of these readings to relative humidity percentage on the slide-rule scale on the case. Relative humidity is a ratio of the amount of water vapor in the air to the amount that would be present if the air were saturated. The term "relative" is used because warmer air can hold more water vapor than cold air. Thus, at the same relative humidity, the actual amount of water vapor in the air at, say, 20°F is considerably less than the amount of water vapor in the air at 90°F. With Permacolor^® red liquid fill instead of mercury in its two thermometers, the 1330PJ is environmentally safe.

The 1330PJ is easy to use. First, you pull the metal shaft from the case to the locked position. Then remove the thermometer slide from the case, rotate the reservoir cover to open it, and fill the reservoir with clean water (distilled water is best), saturating the entire wick. Then close the reservoir cover and snap the slide hook over the extended shaft. Hold the case as shown in the photo on the back of the included instruction sheet, and whirl the thermometer slide as rapidly as possible until the wet bulb temperature falls and then stabilizes. It may take a minute or more until the wet bulb temperature reaches its lowest point. For minimum delay, the water you put in the reservoir should be at ambient temperature. When the wet bulb temperature is at its minimum, read it and also the dry bulb temperature. Then, to obtain the relative humidity reading, insert the thermometer slide into the case with the scale side up. Set the arrow on the slide to the dry bulb temperature. You can then read the relative humidity at the intersection of the RH scale and the wet bulb temperature.

When you finish using the 1330PJ, insert the slide, scale side up, all the way into the case and push the shaft down to lock the slide in place. Be sure to clean the reservoir and clean or replace the wick when these tasks become necessary. Do not expose the 1330PJ to direct sunlight or excessive heat for a prolonged period, or damage may result. Complete maintenance instructions are provided along with sling psychrometer background information and instructions for use.

The two thermometers on the 1330PJ are physically identical. The thermometer scales are on the glass tubes and read from 20°F to 120°F with markers at 1° increments. The case and thermometer slide are both constructed of black high-impact plastic imprinted with white temperature and humidity scales. When closed, the 1330PJ is only 6-7/8 inches long by 1-5/8 inches wide. On the box and on the Taylor website, this instrument is actually called the 1330PJ Pocket Sling Psychrometer.

In addition to the instruction sheet, the 1330PJ Sling Psychrometer comes with a package of six spare wicks. Additional wicks and, if needed, replacement thermometers for the 1330PJ can be ordered from Taylor as indicated in the instructions. Until now, I hadn't played with one of these things since ninth-grade general science with Mr. Paul. The 1330PJ is both inexpensive and accurate. Order one up, and have fun showing your kids (or your grandkids) how relative humidity got measured in the good old pre-digital days!

Features:

• For use at ambient temperatures above 32°F.
• Functionally designed and easy to use and maintain.
• Wet and dry bulb thermometers indicate temperatures in °F.
• Relative humidity scale reads from 10% to 580 RH.
• Environmentally safe (red Permacolor-filled thermometers, no mercury).
• No batteries required.

Specifications:

• Thermometer measuring range: 20°F to 120°F (scales are in 1° increments)
• Dimensions (when closed):
  6-7/8 inches (175 mm) long
  1-5/8 inches (41 mm) wide
  5/8 inch (10 mm) thick