The 3-D printer has become a game changer allowing the repair of older equipment when plastic parts are no longer available. Good job. Have a great week.
You need to be making Kelvin (separate I & V leads) measurements for accurate results below 100 Ohms. Your low resistance standards are designed for it. Use 4 leads, not the fixture to measure your standards.
It should have: "Measurement range of 10 µohms to 100 kohms with 10 µohm resolution." It also has a variable current output, and that would mean a lot when measuring the upper end of the scale. I'm not sure if that variance is automatic with the auto-range on this model.