Lets examine the graph at the beginning of the page. This was taken from a 95 Camaro with a five speed Lenco.
Look for the engine rpm trace. It is the light blue trace starting at 4500 rpm then going to 8200 rpm as the driver went full throttle and onto the limiter. As he dropped the clutch, the revs have flared slightly up to 8600 rpm. This is a because the switch on the clutch pedal that switches on the two step wasn't set quite right. It needed to go off a little later. Because of this, the clutch has hit at 8600 rpm instead of 8200 rpm which is what the crew believed, and it then dragged the revs down to 7200 rpm. The clutch was set a bit too tight for that run and there was very little slip.
See the engine rpm go to 9800 rpm in second gear. The shift light came on at 8600, and that is what the crew believed the shift point was. They had a 1200 rpm over rev.
See the red trace which mostly overprints the blue engine rpm. This is the input shaft rpm taken from a sensor and magnet on the input shaft. At the 5 second mark, it should be overprinted by the green drive shaft rpm, but it does not for the next 1.6 seconds. This is because the Lenco was slipping. Based on this information, the crew overhauled the transmission and it never slipped like this again.
See the magenta spikes at the bottom of the graph. This is the clutch slip. The scale is on the right hand side of the graph.
See the light green trace under it which ends at the Time Zero and restarts at about 8.5 seconds. This is the two step connected to the clutch pedal.
The red bars under that are the shift light.
Without the logger, the crew would never have known they had these difficulties with engine rpm flare on launch, over-rev on the 2 - 3 gear change and slippage in the Lenco.
You can have inexpensive equipment like this so you can monitor these and many more functions like exhaust temperatures, fuel and boost pressures, engine oil and transmission oil pressures, G force and battery volts.