Bacharach 0012-7043 Sling Psychrometer Red Spirit Filled measures percent Relative Humidity (-5° to +50°C) accurately without the complex tables necessary with other analog psychrometers. The wick does not need to be wet with each measurement and a slide rule calculator is included to correlate dry and wet bulb thermometer indications for direct relative humidity readings. Bacharach 0012-7043's case telescopes into the handle for protection when not in use.