Included with your meter
Two reference samples are included with each tint meter. One is lighter (65% to 80%), one darker (20% to 35%). Your meter should read within plus or minus 2% of the printed number on each sample. To verify that the tint meter is working properly, take a reading of the reference samples before use.
Each sample is individually checked on an NIST (National Institute of Standards and Technology) traceable spectrophotometer. They are accurate to within ±1% of the printed value on each label.