The Hach Turbidity Meter, Model 2100P Is a hand-held unit that reliably measures turbidity. Three sample vials and secondary standards are provided. The standards are used to check the calibration of the unit. The sample to be tested is placed in a vial and the vial is inserted into the meter. The cover MUST be closed and the "read" button pushed. Shortly, the turbidity of the sample will be viewed on the display. The range of the meter is 0 to 1000 NTUs.