sighting board मीनिंग इन हिंदी

Where particularly poor background contrast cannot be avoided, a " sighting board " ( usually painted white ) can be placed behind the arm to provide adequate contrast which improves visibility.
Most British road traffic lights are mounted vertically on a black rectangle with a white border ( forming a " sighting board " ) and so dichromats can look for the position of the light within the rectangle top, middle or bottom.