TYPEWRITERS USING THE SAME STYLE AND SIZE OF TYPE ARE DISTINGUISHABLE BY A NUMBER OF TYPES OF DEFECTS. THE MOST IMPORTANT OF THESE IS THE DEFECT CAUSED BY A DAMAGED CHARACTER. THE CASE STUDY INVOLVES AN ATTEMPT TO IDENTIFY AN IBM TYPEWRITER AS THE ONE USED TO TYPE AN ANONYMOUS LETTER. COMPARISONS WERE MADE BETWEEN THE ANONYMOUS DOCUMENT AND A SPECIMEN TYPED ON THE SUSPECTED TYPEWRITER. THE TWO TYPEWRITING SAMPLES SHARED SEVERAL CHARACTER DEFECTS. HOWEVER, THE TWO SAMPLES CONTAINED OTHER DEFECTS THAT WERE UNEXPLAINABLY DIFFERENT. FURTHER INVESTIGATION SHOWED THAT THE UNEXPLAINABLE DIFFERENCES, WHICH PRECLUDED DEFINITE IDENTIFICATION OF THE TYPEWRITER AS THE INSTRUMENT USED TO TYPE THE ANONYMOUS LETTER, COULD BE EXPLAINED BY THE PRESENCE OR ABSENCE OF CARBON PAPER OR A BACKUP SHEET. WHEN TYPEWRITING SAMPLES ARE ANALYZED, THE SAMPLES SHOULD BE PREPARED BOTH WITH AND WITHOUT CARBON COPIES AND BACKUP SHEETS. AS IS THE CASE WITH HANDWRITING SPECIMENS, TYPING SPECIMENS SHOULD BE PREPARED IN THE SAME WAY THAT THE QUESTIONED MATERIAL WAS PREPARED.