Figure 1: 3440 Plus Gauge - Troxler 3430 Manual Of Operation And Instruction

Note the triangular source rod tower. The 3430 Plus, the 3430

Figure 1: 3440 Plus Gauge

Enhanced, and the 3440 Enhanced also have this same tower
design.
By contrast, the "Legacy" versions of the Troxler Model 3430
and 3440 do not have a triangular shaped source rod tower, but
rather a cylindrical, notched index rod parallel to and adjacent
to the cylindrical source rod, neither of which is enclosed in a
tower assembly:
Model 4590 9