The electrode icons on the miHealth are all about calibration and intended point of signal output. Images attached below.
The parallel lines represent the Internal electrodes (normal on body use)
The parallel lines + plug and socket indicates internal and external electrodes live simultaneously
The plug and socket symbol alone is for external accessories (combs , probes etc)
The patch with a lead symbol is for sticky and dry carbon carbon pads
Please be sure to calibrate your device whenever an accessory is attached or removed.