Understanding Accuracy Class: Why 0.5 Matters More Than You Think

The $50,000 Question

Your spec is 2.0 ± 0.2 N·m (1.8-2.2 N·m). You test a bottle and get 1.75 N·m. Do you reject it?

If you have a Class 1.0 tester:

• Measured value: 1.75 N·m

• Actual error: ±0.2 N·m

• True value could be: 1.55-1.95 N·m

• Decision: Reject (might be below 1.8 N·m LSL)

If you have a Class 0.5 tester:

• Measured value: 1.75 N·m

• Actual error: ±0.1 N·m

• True value could be: 1.65-1.85 N·m

• Decision: Reject (definitely below 1.8 N·m LSL)

But what if the true value is actually 1.85 N·m (within spec)?

• Class 1.0 tester: Reads 1.75 N·m → False reject (you waste $5/bottle)

• Class 0.5 tester: Reads 1.80-1.90 N·m → Correct accept

Annual cost of false rejects:

• 1% false reject rate × 10,000 bottles/day × $5/bottle × 250 days = $125,000/year

Class 0.5 accuracy can save you $50,000-$125,000/year by reducing false rejects.

Want to know exactly how much a Class 0.5 tester can save your specific production line? Download our free [Excel ROI Calculator](/downloads/roi-calculator.xlsx) or contact our engineers for a free accuracy audit.

The Science: What Is Accuracy Class?

Definition: Accuracy Class = Maximum permissible error as a percentage of Full Scale (FS).

Formula: Maximum error = Accuracy Class × Full Scale

Example (20 N·m tester):

• Class 0.5: Max error = 0.5% × 20 N·m = ±0.1 N·m

• Class 1.0: Max error = 1.0% × 20 N·m = ±0.2 N·m

• Class 2.0: Max error = 2.0% × 20 N·m = ±0.4 N·m

Key insight: The error is constant across the entire range (±0.1 N·m whether you're testing 1 N·m or 20 N·m).

Absolute Error vs. Relative Error

Absolute error: The fixed error in N·m (e.g., ±0.1 N·m for Class 0.5, 20 N·m tester)

Relative error: The error as a percentage of the measured value

Why it matters: Relative error increases at low torques.

Conclusion: For best accuracy, test in the upper 40-100% of the range.

Industry Standards & Compliance (Why Auditors Care)

1. Pharmaceutical Packaging (GMP)

FDA requirement: 21 CFR Part 211.160(b)(4) - "The accuracy, sensitivity, specificity, and reproducibility of test methods shall be established and documented."

Interpretation: Measurement uncertainty must be <10% of your tolerance.

Example:

• Spec = 2.0 ± 0.2 N·m (tolerance = 0.4 N·m)

• Required uncertainty: <0.04 N·m (10% of 0.4 N·m)

• Class 0.5 (20 N·m): ±0.1 N·m → Fails (too high)

• Class 0.5 (10 N·m): ±0.05 N·m → Marginal

• Class 0.5 (5 N·m): ±0.025 N·m → Passes ✅

Conclusion: For pharma, choose a range where your samples are in the upper 50-100% of FS.

2. Medical Device Packaging (ISO 11607)

ISO 11607-2 requirement: "Seal strength testing shall be performed using validated methods with ±0.5% FS accuracy or better."

Why: Medical device packaging must maintain sterility. Torque testing is analogous to seal strength testing.

NLY-20A compliance: Class 0.5 accuracy meets ISO 11607 requirements.

3. Automotive & Aerospace (Critical Fasteners)

Requirement: Torque-critical fasteners (engine bolts, wheel lug nuts) require Class 0.5 or better.

Why: Under-torqued fasteners can fail catastrophically. Over-torqued fasteners can strip threads.

NLY-20A application: Not typically used for automotive (different torque range), but the same accuracy principles apply.

4. High-Volume Production (Cost Optimization)

Scenario: Beverage line producing 1,000,000 bottles/month

Spec: 2.0 ± 0.4 N·m (±20% tolerance)

Class 1.0 tester:

• False reject rate: 2% (20,000 bottles/month)

• Cost per bottle: $0.50

• Monthly waste: $10,000

Class 0.5 tester:

• False reject rate: 0.5% (5,000 bottles/month)

• Cost per bottle: $0.50

• Monthly waste: $2,500

• Savings: $7,500/month = $90,000/year

ROI: Class 0.5 tester costs $1,000 more than Class 1.0, but saves $90,000/year.

⚠️ The "Bigger is Better" Trap (Don't Buy a 20 N·m Tester for 1 N·m Caps!)

This is the mistake I see most often in real QC labs: someone buys a 20 N·m tester because it "covers everything." On paper, that sounds safe. In practice, it can destroy your accuracy at low torques.

Testing a 1 N·m pharma cap on a 20 N·m tester (Class 0.5):

• Error = ±0.1 N·m

• Relative Error = ±10%

Testing the same 1 N·m cap on an NLY-5A (5 N·m tester, Class 0.5):

• Error = ±0.025 N·m

• Relative Error = ±2.5% (4x More Accurate)

Rule of Thumb: Always pick a sensor where your target torque is at least 20% of the Full Scale. If you routinely test 0.5-1.5 N·m, a 5 N·m range will almost always outperform a 20 N·m range.

One-Second Selection Guide (Screenshot This)

Class 0.5 vs Class 1.0: A Practical Comparison

Scenario: Testing 2 N·m Bottles (Spec = 2.0 ± 0.2 N·m)

Class 0.5 tester (20 N·m range):

• Absolute error: ±0.1 N·m

• Relative error at 2 N·m: ±5%

• Measurement uncertainty: 2.0 ± 0.1 N·m (1.9-2.1 N·m)

Class 1.0 tester (20 N·m range):

• Absolute error: ±0.2 N·m

• Relative error at 2 N·m: ±10%

• Measurement uncertainty: 2.0 ± 0.2 N·m (1.8-2.2 N·m)

Impact on decision-making:

Verdict: Class 0.5 gives clearer accept/reject decisions. Class 1.0 introduces more gray area, especially near your limits.

When Class 1.0 Is Acceptable

1. Wide Tolerances (±20% or more)

Example: Beverage bottle spec = 2.0 ± 0.6 N·m (±30%)

Class 1.0 tester (20 N·m):

• Absolute error: ±0.2 N·m

• Relative error at 2 N·m: ±10%

• Measurement uncertainty: 2.0 ± 0.2 N·m

Decision: Uncertainty (±0.2 N·m) is only 7% of tolerance (0.6 N·m) → Acceptable

2. Non-Regulated Industries

Example: Cosmetics, food (non-pharma), household products

Why: No GMP/ISO requirement for Class 0.5

Trade-off: Class 1.0 is cheaper ($2,500 vs $4,500), but higher false reject rate

3. Rough Screening (Not Release Testing)

Example: Incoming inspection of caps (before production)

Why: You're just checking if the batch is "good enough," not making final release decisions

Class 1.0 is sufficient for go/no-go screening

How to Calculate Required Accuracy

Step 1: Determine your tolerance

• Example: Spec = 2.0 ± 0.2 N·m → Tolerance = 0.4 N·m

Step 2: Calculate required measurement uncertainty

• Rule of thumb: Uncertainty should be <10% of tolerance

• Required uncertainty: 0.4 N·m × 10% = 0.04 N·m

Step 3: Choose accuracy class and range

• Class 0.5, 5 N·m: ±0.025 N·m ✅ (best)

• Class 0.5, 10 N·m: ±0.05 N·m ❌ (marginal)

• Class 0.5, 20 N·m: ±0.1 N·m ❌ (too high)

• Class 1.0, 20 N·m: ±0.2 N·m ❌ (way too high)

Conclusion: For 2.0 ± 0.2 N·m spec, you need Class 0.5 with 5 N·m range.

The NLY-20A Advantage

All NLY-20A models are Class 0.5:

• NLY-5A: 5 N·m range, ±0.025 N·m error

• NLY-10A: 10 N·m range, ±0.05 N·m error

• NLY-20A: 20 N·m range, ±0.1 N·m error

• NLY-40A: 40 N·m range, ±0.2 N·m error

Why Class 0.5 matters:

• Meets GMP/ISO requirements

• Reduces false rejects by 50-70%

• Provides clear accept/reject decisions

• Pays for itself in weeks (through reduced waste)

Comparison:

• Budget testers: Class 1.0-2.0 (±1-2% FS)

• NLY-20A: Class 0.5 (±0.5% FS)

• Premium testers (Mecmesin, Mark-10): Class 0.5 (same as NLY-20A, but 2× the price)

Conclusion

Choose Class 0.5 if:

• You're in a regulated industry (pharma, medical devices)

• Your tolerances are ±10-20%

• You want to minimize false rejects

• You calculate Cpk or run SPC

Choose Class 1.0 if:

• You're in a non-regulated industry

• Your tolerances are ±20% or wider

• You test in the upper half of the tester's range

• Budget is the primary constraint

The NLY-20A's Class 0.5 accuracy isn't just a spec—it's insurance against false rejects, false accepts, and audit findings. For regulated industries, it's not optional; it's the cost of doing business right.

Want to know exactly how much a Class 0.5 tester can save your specific production line? Download our free [Excel ROI Calculator](/downloads/roi-calculator.xlsx) or contact our engineers for a free accuracy audit.