The values for TVOC and eCO2 on Mill Sense depend on a calibration period to become accurate.
When connecting a Mill Sense for the first time, it will take 72 hours before it displays these values. If you move the unit to a new location, it may take several days before the correct values can be measured - Up to five days.
If the values shows 0, then you have to take this on warranty, because it might be some damage on the sensor.