The Scanmaster allows you to monitor what the ECM sees such as air intake temp, coolant temp, engine rpms, miles per hour, if there are any malfunction codes in the ECM, IAC position....there's a few others i can't think of right now....when you mash the gas pedal and the TPS gets to 3 volts, the Scanmaster goes into a "record" mode to allow you to see if you encountered any knock retard as well as at what mph and the 02 millivolts at the time. In the "standby" mode it shows the 02 millivolts as well as if the ECM is pulling any timing.
As for the Caspers gauge, I also recommend the knock alarm. You can hide it anywhere (I have mine under the radio pod facing the driver side floor board) and as long as you don't have the radio blasting, you can hear it when it goes off. It will detect if the knock sensor has picked up something before the Scanmaster will show if it's pulling timing to do the job.
