After more than a century measuring everything from nanometers to the purity of sugar, managers at the National Institute of Standards and Technology (once called the National Bureau of Standards), decided to do a bit of spring cleaning. In the process, they discovered hundreds of custom-made devices and machinery that lack records about what exactly they were used for. So they are turning to the public for help. Engineering enthusiasts and gadget freaks are urged to visit a new Web site and see if they can help identify any of the 137 scientific instruments posted on the site or provide information as to how they were used. NIST says they will post images of hundreds more unknown instruments in the coming months.