Hand held scanners usually come in two forms, 3D and document scanners. Hand held scanners are manual devices/units which are passed over the surface of the image which requires scanning. Hand held scanners when used in this way require a steady hand, as any uneven movements of the scanning rate will result in the distortion of the scanned image. For this reason, most Hand held scanners will usually have a small light or indicator, to notify the user if the scanning action is too fast. A typical hand held scanner will have a small viewing window, through which the document being scanned can be viewed. Hand held scanners were popular in the 1990s but has since waned, but the use of 3D scanners still remains popular for many applications such as inspection and analysis, reverse engineering and medical applications.