Each Data log Field is based on an OutputChannel.
There are 2 types of Outputchannels
1. Controller Channels - values contained in the runtime data stream received from the controller.
2. Expression based Channels - new channels based on any other channels or Constant using mathematical operations and TunerStudio functions.
Type 1 are primarily used by Firmware developers as they are read directly from the controller, type 2 are created by combining or altering type 1 in mathematical expressions, they can be added to the ini file by firmware developers or be user extensions.
TunerStudio can only really tell the controller to log what it know, and at the time of transformation into a normal data log really only know what type 1 fields were selected. So, if you add a Type 2 field, it will actually add all the dependent channels. Or if you have all the fields needed to create a type 2, that will automatically come along for the ride.
Then when it displays what is going to be logged, it will display all the fields that it can and will recreate when the raw SD data is transformed into a normal data log.