Threshold limit value

how to define threshold limit value. how to effect low or high…??

Need more clarification for Threshold limit… with respect to what?
Thanks

threshold limit is very litter amount of error before starting the measurement.
So you can only calibrate that instrument and used it with zero error.

Sorry but this is not about to instrument calibration related question. This is about solvents exposer type question.and I need more clarification about TLV.