James Royse commented on the singular role which duplicate manuscripts can play in textual criticism saying that they provide “the best possible case” to access a scribe’s habits and that by using Abschrift manuscripts “we can virtually look over the scribe’s shoulder.” He then mentions that 0319, which copies Claromontanus (D06), is our earliest example of such a manuscript. Claromontanus is the only extant New Testament manuscript to have two known duplicates in 0319 (ninth century) and 0320 (tenth century). 0319 and 0320 are also the only known duplicate majuscule manuscripts. This paper analyzes test passages of 0319 and 0320 in order to determine the scribes’ habits. The shocking conclusion is that neither 0319 nor 0320 add or omit any text in the test passages. These scribes make many orthographic and other variants but they make very few significant substitutions and no additions or omissions. I have analyzed these manuscripts as duplicate manuscripts and I have also analyzed these manuscripts using the singular readings method. The result is that I am able to compare the resulting scribal habits when using the duplicate manuscripts method against the scribal habits when using the singular readings method. Duplicate manuscripts such as 0319 and 0320 have historically been ignored for the very reason that they are copies of a known manuscript. While it is correct to exclude a manuscript from critical editions when we can know that it is a copy, it is not sufficient to ignore them altogether. While the text they contain is dependent upon another known text, these manuscripts contain useful information concerning the nature of scribal copying. There are, at the moment, fourteen manuscripts for which we know the Vorlage but there are surely more of which we do not yet know. After analyzing many duplicate manuscripts I have charted their scribal habits through time and will comment on their textual stability in light of Constantine. One unavoidable disadvantage of previous studies on scribal habits is that they, of course, do not have access to the Vorlagen of early manuscripts. They therefore must postulate what the Vorlage probably said and then base conclusions concerning scribal habits off of the hypothetical Vorlage. While such hypothetical reconstructions are unavoidable, the duplicate manuscript method is to be preferred, when possible, because it requires no hypothetical reconstructions and we can get to the actual habits of these scribes. The enormous disadvantage of the duplicate manuscripts method is that there are very few sets of duplicate manuscripts and most of them are very late with the ninth-century 0319 being the earliest.