Gita Bhandari

I generate one code by hand before generating any with a tool, because the check digit calculation is what a tool hides and a retailer enforces. The retail ones are thirteen and twelve digits including the check digit, and the leading digit encodes the product type and the manufacturer, which is why a barcode generated with the wrong leading digit is rejected by a scanner database rather than by a checksum. The check digit is computed by weighting the digits alternately with three and one from the right, summing, and taking the complement to ten. The result is a single-digit check on a transcription error, and it is verified on scan. A code with the wrong check digit fails at the scanner, which is the cheapest possible failure and the one most generators get right. The quiet zone is the margin of light modules around the code. It is part of the specification and scanners are entitled to refuse a code without it, which is why the same generator produces readable and unreadable codes depending on whether that margin was set. I finish on the difference between a barcode and a QR code for this purpose, since one encodes a number that a database resolves and the other encodes data the reader already has. The scan quality requirements are separate from the symbology. A code printed too small, on a curved surface, or with insufficient contrast fails for reasons that have nothing to do with its digits being right. The quiet zone is part of the specification rather than a margin, which is the distinction that catches people out.