His worrying about where a pot came from and what period it dated to and what that meant to the other objects buried with it were light-years away from the ideas represented in this photo dated to 1800, in which "Egyptian pots" was considered enough information for the thinking man.
Petrie was a scientific archaeologist, probably close to our first example.
Archaeologically, you would expect no 78s to be found in a junkyard that was closed before 78s were invented.
There might be a small number of them (or fragments of them) in the junkyard which stopped taking junk during the first years 78s were invented.
What this step does is create a visual representation of the qualities of the artifacts, and their co-occurrence at different junkyards.
Notice that this figure does not mention what kind of artifacts we're looking at, it just groups similarities.
Petrie's problem was that he had discovered several predynastic cemeteries along the Nile River in Egypt that seemed to be from the same period, but he needed a way to put them in chronological order.Larger percentages of artifact types are illustrated with longer bar snippets and smaller percentages with shorter bar snippets.A good source of information about how to make charts in Excel is Ted French's Excel Chart Tutorial (for several different versions of Excel).We don't have historical information about the junkyards--they were illegal dumping areas and no county records have been kept on them.For a study we're doing on, say, the availability of music in rural locations during the 20th century, we'd like to know more about the deposits in these illicit junkyards.