Abstract: There is disclosed a wallpapering aid comprising a base having a ground engaging portion, and a support. The support is configured to extend from the base and, in use, bear against a sheet of wallpaper hanging from a height above the support to cause a lower region of the sheet of wallpaper to hang offset horizontally from an upper region of the sheet of wallpaper. The wallpapering aid may be used to facilitate the preparation and fixing of the sheet of wallpaper to a wall.

Abstract: An optical system for measuring relative lateral displacement or velocity relative to a surface above which the system is independently supported has a grating consisting of different bands that are adapted to impart to incident light received from the surface two different optically selective characteristics such as different polarizations or different wavelengths. Light transmitted by or reflected from the bands is focussed through filtering means onto photodetectors which produce signals proportional to the light received thereby. The filtering means (polarization selective or wavelength selective, as the case may be) associated with the respective photodetectors respectively separate light coming from bands having one of said characteristics from light from the bands having the other of said characteristics.