CST Weights & Measures Certification 3 — Questions and Answers
Question 1: What is the primary purpose of a 'shift test' when inspecting a commercial platform scale?
- To test the scale under maximum load conditions
- To detect errors caused by off-center placement of loads (Correct answer)
- To verify the scale's tare mechanism
- To measure the scale's response time
Correct answer: To detect errors caused by off-center placement of loads
The shift test places test weights in different zones of the platform to detect corner or section errors caused by uneven load distribution.
Question 2: Under NCWM guidelines, who has legal authority to enforce weights and measures laws at the state level?
- NIST field inspectors
- State weights and measures officials (Correct answer)
- County health departments
- The Federal Trade Commission
Correct answer: State weights and measures officials
Weights and measures enforcement in the U.S. is primarily a state and local responsibility, carried out by state and county weights and measures officials.
Question 3: What class of weights is typically required for testing Class III commercial retail scales?
- Class F (Field Standard) (Correct answer)
- Class S (Scientific)
- Class E2 (European reference)
- Class OB (avoirdupois bulk)
Correct answer: Class F (Field Standard)
NIST Handbook 105-1 specifies that Class F field standard weights are appropriate for testing Class III commercial devices in the field.
Question 4: A scale technician recertifies a vehicle scale after repairs. Which document must be completed and provided to the scale owner?
- A NIST Form 37-B calibration certificate
- A Certificate of Conformance from NTEP
- A calibration report or service record documenting the work performed (Correct answer)
- An EPA environmental compliance form
Correct answer: A calibration report or service record documenting the work performed
After service or calibration, the technician must provide documentation — typically a calibration report — describing the work done, standards used, and results obtained.
Question 5: What is the significance of 'traceability to national standards' in scale calibration?
- The scale must be manufactured in the United States
- Calibration results can be linked to NIST reference standards through an unbroken chain of comparisons (Correct answer)
- The scale must be registered with a national database
- The calibration must be performed by a federal employee
Correct answer: Calibration results can be linked to NIST reference standards through an unbroken chain of comparisons
Metrological traceability means that calibration measurements are related to national (NIST) or international references through a documented, unbroken chain of comparisons with stated uncertainties.
Question 6: A livestock scale with a 20,000 lb capacity and 10 lb divisions is tested and found to have an error of 30 lb at mid-range. Under NIST Handbook 44, is this within the MAE?
- Yes, 30 lb is within 0.1% of capacity
- No, the MAE for this scale is 20 lb (2 divisions) (Correct answer)
- Yes, livestock scales have a 50 lb tolerance
- No, all vehicle scales must read within 5 lb
Correct answer: No, the MAE for this scale is 20 lb (2 divisions)
For a Class III scale with 10 lb divisions, the MAE is one scale division (10 lb) at minimum, so a 30 lb error at mid-range (where MAE may be 1–2 divisions depending on the load range) exceeds tolerance.
Question 7: What is meant by 'zero-load reference value' on an electronic scale?
- The weight of the empty scale platform recorded during manufacturing
- The scale's indication when no load is applied, used as a baseline for measurements (Correct answer)
- The minimum test weight required for calibration
- The scale's power consumption at idle
Correct answer: The scale's indication when no load is applied, used as a baseline for measurements
The zero-load reference value is the scale's reading when unloaded, serving as the reference point from which net weight indications are derived.
CST Weights & Measures Certification 3
What is the primary purpose of a 'shift test' when inspecting a commercial platform scale?