Due to the high voltages involved in secondary ignition systems, it is not possible to make measurements by direct connection; attempting to make a direct connection will almost certainly damage the measuring instrument.
The PP178 is a capacitive pickup that simply connects around the insulation of an ignition circuit component such as a plug wire — this avoids the need for direct connection.
The PP178 comes with a shielded 2.5m (100 inch) lead. It is suitable for use with conventional ignition systems and most HEI and DIS systems.
Although ideal for use with a Pico automotive oscilloscope, the PP178 pickup can also be used with most other makes of oscilloscope provided they have an waveform invert option.