In the course of your data collection with BACtrack Skyn, you may encounter some negative TAC values. Please see the below descriptions of two different patterns of negative TAC values you may see.
Type One:
Small negative values are often due to small influences of environmental disturbance, or potentially just minor variations in the calibration process of the Skyn sensors. As long as the negative values are small, they can effectively be considered as 0 values.
Type Two:
In a general sense, larger negative values represent an instance where something in the collected sample (at that data-point) causes the signal sensitivity to be lower than a normal air sample in the absence of any alcohol. To be clear, it is not the case that Skyn detected negative amounts of alcohol in a sample (this is not possible). Instead, something in the collected air sample is interacting with the sensor to decrease signal output more than would be expected in a normal air sample with no ethanol present.
It is possible that extended periods of wear without any ‘rest time’ for the Skyn sensor (i.e. time where Skyn is not worn and not closely adhered to the human wrist) can cause a bit of moisture build-up and potentially impact sensor behavior.