Hygrograph

This instrument is manufactured as per IS: 5900-1970.
The humidity sensor consists of a bundle of Human Hair held between two adjustable jaws, the whole assembly being mounted on a hair movement plate.
The variations with length of the hair stands due to changes in the relative humidity are measured by the displacement of the centre of the hair strands transmitted by a lever and a pair of cams to the pen arm so that the movement of the pen is a linear function of the relative humidity.
Available with mechanical clock .