SPY 780: Capable of reading 1,000 to 5,000 volts the SPY 780 is designed to be used with thin film coatings. SPY 785: Capable of reading 1,000 to 15,000 volts the SPY 785 is designed to be used for thicker coatings such as coal tars, extruded, and tape coatings. SPY 790: Capable of reading 5,000 to 35,000 volts the SPY 790 is designed to handle a very wide range of coating thicknesses and types.