Cartool and import Biosemi file

[Michaël Mouthon]

Denis ans others, I would like to understand how Cartool manage the .bdf file of Biosemi. 

In the EEGlab manual, it is strongly advice during .bdf import to re-reference the signal to an electrode. See the following sentence: 

"Systems with active electrodes (e.g. BIOSEMI Active Two), may record data reference-free. In this case, a reference be must be chosen post hoc during data import. Failing to do so will leave 40 dB of unnecessary noise in the data!" (https://irenevigueguix.wordpress.com/2016/07/07/eeglab-tutorial-re-refering-eeg-data/)

So my question: when we open a raw bdf file with Cartool, does Cartool reference the signal to an electrode ? If yes, which one ? 

Or Cartool display the raw value recorded in the bdf file. 

Thank you in advance for the basic question.