Hand powered relative humidity measuring device (%RH) .Rotate to provide adequate and consistent ventilation of the bulbs.Environmentaly friendly blue thermometer tubes with LO-tox filling.Similar accuracy as mercury but with clearer legibility.Range: -5 to +50C.Accuracy: +/- 1C.Resolution: 0.5C.This instrument uses shorter tubes and the design incorporates a 'slide rule' type calculator to determine the % of relative humidity.Body of the instrument slides away into the handle providing complete protection when not in use.L x W x D: 210 x 36 x 16mm.