This applies to the 3900, 3905, 8900, 8905, 8950, 800, 850, 500, 550, 100
The 390x CCD scanners are contact scanners, they must be physically touched to the barcode you are scanning.
The Wasp CCD LR (89xx, 8xx,500, 550, 100) (long range) scanner is an exception - it can be held 12 to 15 inches away from the barcode, depending on the barcode's density and size.