While in the data logging screen, press the [Tab] key. You should see a list of sensors appear. Use the arrow keys to select the sensor for auto-triggering. RPM is a bit tricky to use as an auto-trig sensor. The first "RPM" is indexed as 0 (zero) and is not useable for auto-triggering. The "Scaled RPM" is useable but its full scale value is determined by the "Table Cell Width" programmed in the configuration. If you multply this value by 16, the result will be the full scale Scaled RPM value. To select the auto-trigger value for Scaled RPM, press the [A] key and enter the percentage of the full scale value that corresponds to you desired trigger RPM.