Abstract: A portable tester for determining the primary winding to secondary winding current ratio of a current transformer while that transformer is in service, including a current probe having a split core positionable around an active power line supplying current to the transformer, an AC to DC converter to convert the AC output of that probe to a first DC signal, another AC to DC converter for converting the secondary output of the current transformer under test to a second DC signal, and a ratio meter for converting the first and second DC signal into a visual display of the ratio of those signals. A mechanism is provided for assuring proper location of the decimal point on the ratio meter. Polarity and burden testing is also provided.