Doble is the leading manufacturer of many types of electrical testing devices, so the tests that are carried out using them are associated with the term Doble testing. Doble equipment puts an AC signal of 2.5kV or 10kV on the test specimen, mostly a transformer, and then it measures signals in proportion to watts. After that you can directly read or calculate from the instruments. A perfect insulation carries only capacitive current and hence its power factor is zero. A dirty, wet, or leaking instrument will have a leakage current, hence raising power factor by 0.1%, but it is all relative.
Doble offers different types of electrical test equipment is probably the most widely used.
A Doble test sequence is capable of making many measurements, just like the readings of a transformer: Low to High & Ground, High to Low & Ground, and others using guards inputs. It is a sensitive device and hence requires precision in order to get perfect readings, and to accurately account for factors like temperature. Doble also supplies a database containing readings of all the transformers that can be tested using their units. This gives the customer a handbook for comparing the readings he took, and judge them using similarities in size, type, and manufacturer. When previous results are compared with new results, users can get a better understanding of the system.