A number of cases in which the author was involved pertained to the splitting of paper currency and regluing the fronts and backs of bills to the fronts and backs of lesser denominations. Typically, the fronts and backs of $20 bills would be glued to the split fronts and backs of $2 bills, with the bills being passed as two $20 bills (the bills would be passed to retailers with the $20 front or back side showing). The forensic work done consisted not only of obtaining evidence in specific cases but also in the testing of various potential papers that could be used for currency to prevent "splitting." Another case consisted of the deciphering of typewriter impressions on several pieces of well-used and badly crumpled carbon paper found in a suspect's wastebasket. The document was rendered readable by placing the carbon paper in a copying frame that resulted in a mirror-like reflection. Then, working with the aid of a vacuum cleaner and a sheet of perforated board, a suction box was built to remove the wrinkles. Next, the copying lights were reversed to face the camera and a large sheet of white cardboard was placed across the front of the copying camera with a hole cut in the middle to allow the lens to protrude and a shade to prevent light from striking the lens. A photo of the carbon paper was produced to make the typewriter letter impressions come out black while the background was rendered white. Another case involved document analysis of invoices in a case where it was suspected that cooked meat, on which tax was payable, had been billed as fresh meat, on which tax was due. A number of cases involved the matching of torn or perforated paper ranging from the perforated edges of postage stamps on a threatening or obscene letter to matching the torn edge of a piece of scribbler paper that contained kidnap threats to a member of Parliament. Other cases consisted of the deciphering of enemy censorship cancellations, passport analysis, narcotics cases that involved documents, and searches for concealed messages and micro-dots.