While the Taint Detector is in your inventory or hotbar it will display the level of Taint in your current chunk in the lower right-hand corner of the screen. If the dark sphere below the bar glows it indicates that the current chunk might increase it's Taint rating due to things like hidden Taint Crystals, or possibly even lower its Aura rating.
As rule of thumb, each segment of the bar in the lower corner indicates 2000 units of taint in the current chunk. 3 segments of Taint and a low level of Aura can convert the chunk into a Tainted Zone
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