Sling Psychrometer Relative Humidity Indicator by Bacharach

Accurately indicates percent relative humidity without charts or formulas.

Starting at $38.00

Sling Psychrometer Relative Humidity Indicator
Grouped product items
Product Name Qty
Replacement Thermometer Only, Red Spirit Filled, Model 12-0266, by Bacharach
Sling Psychrometer, Model 12-7012 Red Spirit Filled, by Bacharach


The compact Bacharach Sling Psychrometer uses the accurate wet bulb-dry bulb thermometer principle to provide a simple, rapid measurement of relative humidity without tables, charts, or formulas. 

Portable and non-electronic, the sling psychrometer consists of two thin bulb thermometers and a refillable water reservoir in a high-strength plastic case. There is no need to wet the wick each time a reading is made. The case is simply whirled freely in the hand; wet and dry bulb temperature readings are taken; and percent relative humidity is determined from the built-in slide rule on the handle. When not in use, the thermometer case telescopes into the handle for protection.

Thermometers in sling psychrometers are filled with non-toxic red spirit (alcohol) and are calibrated in °F.



  • Easy to use and designed for portability.
  • Slide rule construction quickly converts temperature to relative humidity.
  • Built-in reservoir holds sufficient water for several hours of testing.
  • Thin thermometer bulb gives fast thermal response.
  • Thermometers constructed of shock-resistant glass.
  • Stems have deep-etched numerals and 1° scale divisions for easy reading.
  • Inexpensive, reliable and accurate.


The Sling Psychrometer can be easily operated by following these steps:

  • Be sure the wick on the wet bulb is clean and saturated with water while the bulb on the other thermometer is dry.
  • Whirl the Psychrometer body at a rate of two or three revolutions per second (120 to 180 RPM) for a minimum of 1½ minutes to allow the thermometer indications to stabilize.
  • Immediately read the wet bulb temperature first and then the dry bulb temperature.
  • For dry bulb temperatures above 70°F (21°C), use the high range scale on the sleeve-handle. If the dry bulb temperature is below 70° (+21°C), use the low range scale.
  • Set the wet and dry bulb temperatures opposite each other on slide rule and read %RH on the lower scale.


Sling Psychrometers have many applications in commercial and industrial applications. Some of these are:

  • Hospitals
  • Computer rooms
  • Laboratories
  • Industrial plants
  • Colleges and schools
  • Critical storage areas
  • Manufacturing plants
  • Air conditioned environments
  • Athletic & sport programs


  • Thermometer Divisions: 1°F
  • Dimensions: 7½" long x 1" diameter
  • Accuracy: ±5% RH

Ordering Information

Order No.
Order No.
4 wicks, 10" long
Order No.
12-7012 +20 to +120°F Red Spirit 12-0266 12-0011