The pBR322 convention
pBR322 is a distant ancestor of pET28a. If you compare the two maps below you will see that they have the same replicon labelled as ori or pBR322_origin.

The map of pBR322 is shown in the conventional orientation: the single EcoRI site is at coordinate 0/4359 and numbering proceeds in a clockwise direction through the BamHI site. The map of pET28a is presented with the pBR322-derived ori element in the same orientation (note the labelling of a pBRrevBam_primer also). Because of the way that the pET vectors were built, this means that in the conventional depiction the expression region runs counter-clockwise.