In scientific measurements, the terms “precision” and “accuracy” are often used interchangeably. However, they have distinct meanings and implications. Understanding the difference between precision and accuracy is crucial for interpreting data correctly and improving measurement techniques.
Precision vs Accuracy Definition
Accuracy refers to how close a set of measurements are to the true value. It describes systematic errors and can be seen as a measure of statistical bias. High accuracy requires both high precision and high trueness (the closeness of the average of measurements to the true value).
Precision refers to how close the measurements are to each other, describing random errors or the statistical variability. It is a measure of the repeatability or consistency of the measurements.
In simpler terms:
- Accuracy: The average of measurements is close to the true value.
- Precision: The measurements are closely clustered together with low variability.
To illustrate, think of a dartboard: the bulls-eye represents the true value. Darts that land close to the bulls-eye are accurate, while those tightly clustered show precision. Here’s how it breaks down:
- Neither Accurate Nor Precise: Darts aren’t near the bulls-eye and aren’t clustered. (As shown in Figure A)
- Precise But Not Accurate: Darts tightly clustered but away from the bulls-eye. (As shown in Figure B)
- Accurate But Not Precise: Darts evenly spaced around the bulls-eye but not clustered. (As shown in Figure C)
- Both Accurate and Precise: Darts close to the bulls-eye and tightly clustered. (As shown in Figure D)
Significant Figures and Scientific Notation
Accuracy and precision are often implied by significant figures:
- A recording of 843.6 m implies a margin of error of 0.05 m.
- Scientific notation can clarify significant figures, e.g., 8.0 × 10³ m indicates a margin of 50 m.
Repeatability and Reproducibility
- Repeatability: Variation using the same instrument and operator in a short time period.
- Reproducibility: Variation using different instruments and operators over a longer time period.
In engineering, precision is often taken as three times the standard deviation of measurements, indicating that 99.73% of measurements fall within this range.
ISO Definition (ISO 5725)
According to ISO 5725-1:
- Trueness: The closeness of the mean of a set of measurements to the true value.
- Precision: The closeness of agreement among a set of results.
ISO standards avoid the term “bias” due to its different connotations outside science and engineering.
Which is More Important, Accuracy or Precision?
The importance of accuracy versus precision depends on the context. In machining parts, both ensure the quality of the product and customer satisfaction together.
- Accuracy refers to how close a measurement is to the true value. It’s crucial when you need to ensure that your results are correct and reliable.
- Example: For example, if a part is designed to be 10 centimeters in length and the machined part measures 10.1 centimeters, the accuracy is lower because it deviates from the design dimension.
- Precision refers to the consistency of measurements. Precise measurements are vital for tracking progress and making incremental improvements.
- Example: If multiple parts are machined and their dimensions are consistently close to each other (e.g., 10.01 centimeters, 10.02 centimeters, 10.00 centimeters), this indicates high precision in the machining process.
Balancing accuracy and precision is crucial in machining:
- Importance of Precision: Ensures consistent and stable dimensions across all machined parts, facilitating process control and maintaining product quality.
- Importance of Accuracy: Ensures machined parts meet design specifications closely, ensuring functionality and performance align with expectations.
What is the Difference Between Precision and Tolerance?
Precision and tolerance are crucial concepts in manufacturing and design. Precision refers to the degree of exactness or refinement in a measurement, whereas tolerance signifies the allowable deviation from a specified dimension.
| Aspect | Precision | Tolerance |
|---|---|---|
| Measurement | High degree of accuracy | Permissible range of deviation |
| Machining | Ensures consistent and exact results | Allows for slight variations |
| Example | +/- 0.002 mm (very precise measurement) | +/- 0.1 mm (standard tolerance in machining) |
What is the Difference Between Accuracy and Tolerance?
Accuracy and tolerance are critical concepts in manufacturing and engineering, defining the quality and precision of machined components.
| Concept | Definition | Importance | Example |
|---|---|---|---|
| Accuracy | How close a measurement is to the true value. | Ensures parts meet exact specifications for functionality. | Engine components require precise dimensions for optimal performance. |
| Tolerance | Allowable deviation from a specified dimension. | Defines acceptable variation without compromising function. | Engine parts have tighter tolerances; door handles can have broader tolerances. |
In machining, adherence to tolerance limits (e.g., 0.001635 mm for flat and perpendicular surfaces, 0.003175 mm for curved surfaces) ensures consistency and reliability in part production. Balancing accuracy and tolerance optimizes manufacturing efficiency and product quality.
Examples of Accuracy vs. Precision In Machining
In machining processes, achieving both high precision and accuracy ensures that manufactured parts meet stringent engineering specifications for quality and performance.
Precise and Accurate
Precision refers to the consistency of measurements, while accuracy relates to how close measurements are to the target value. In machining, achieving both precision and accuracy ensures high-quality parts. For example, imagine a CNC machine tasked with drilling a hole 70mm from an edge, with a tolerance of +/- 1mm. If the machine consistently drills holes measuring between 69.5mm and 70.5mm across multiple production batches, it demonstrates precision (consistent results) and accuracy (closeness to the intended 70mm).
Not Precise but Accurate
Sometimes, parts may be accurate in meeting the target dimension but lack precision due to variability. For example, consider piston manufacturing where the target height is 1.2 inches with a tolerance of +/- 0.005 inches. Some pistons may measure between 1.195 inches and 1.205 inches, while others fall outside this range. Despite being accurate (falling within the specified tolerance), the process lacks precision because of the variability in measurements.
Precise but Not Accurate
Precision without accuracy occurs when measurements are consistently close to each other but consistently deviate from the target value. For instance, if pistons are consistently manufactured to heights of 1.21 inches, 1.22 inches, 1.21 inches, and 1.215 inches, but the target height is 1.2 inches with a tolerance of +/- 0.005 inches, the process demonstrates precision (consistent measurements) but lacks accuracy (the average measurement does not match the intended dimension).
Not Precise and Not Accurate
When neither precision nor accuracy is achieved, machining produces parts that vary widely from the target dimensions. For example, aiming for a 20mm plastic piece with a tolerance of +/- 0.5mm but obtaining parts measuring 18mm, 22mm, 19mm, 17mm, and 21mm, indicates both imprecision (varying measurements) and inaccuracy (deviation from the intended 20mm).
Accuracy vs Precision In Machining: Differences
When it comes to the difference between precision and accuracy in processing, this table clearly compares their features.
| Feature | Precision | Accuracy |
|---|---|---|
| Definition | Represents the consistency and repeatability of measurements. | Represents how close measurements are to the true or intended value. |
| Example | CNC machine drills consistently within a narrow range, e.g., ±0.05mm. | CNC machine consistently drills holes around 50.0mm, meeting the intended 50mm mark. |
| Emphasis | Focuses on the reliability and consistency of measurements. | Emphasizes correctness and proximity of measurements to the target value. |
| Assessment | Assessed by the variability or spread of measurements. | Evaluated by comparing measurements to a known standard or target value. |
| Goal | Ensures consistency and reproducibility in part dimensions. | Ensures parts meet design specifications and functional requirements. |
| Application | Critical for precision machining operations, like manufacturing precision mechanical components. | Essential across industries to ensure products meet stringent design and standards requirements. |
Benefits Of Accuracy And Precision In Part Production
Accurate and precise part production in manufacturing offers several significant benefits that contribute to overall quality, efficiency, and customer satisfaction. Here are some key benefits of accuracy and precision in part production:
- Quality Assurance: Accurate and precise manufacturing ensures that parts meet exacting design specifications and tolerances. This reduces the likelihood of defects and ensures consistent product quality.
- Reduced Scrap and Rework: By producing parts that are both accurate and precise, manufacturers minimize scrap material and the need for costly rework. This leads to lower production costs and improved efficiency.
- Improved Performance: Parts manufactured with high accuracy and precision perform better in their intended applications. They fit together seamlessly, operate reliably, and meet customer expectations for reliability and durability.
- Enhanced Reputation: Consistently delivering accurate and precise parts enhances a manufacturer’s reputation for quality and reliability. This can lead to increased customer satisfaction, repeat business, and positive word-of-mouth referrals.
- Cost Savings: Precision manufacturing reduces material waste, rework costs, and the need for post-production adjustments. Over time, this leads to significant cost savings for the manufacturer.
- Compliance and Standards: Accurate and precise manufacturing ensures compliance with industry standards, regulatory requirements, and customer specifications. This is particularly crucial in industries such as aerospace, automotive, and medical devices.
- Operational Efficiency: When machines and processes are calibrated to deliver accurate and precise results, overall production efficiency improves. This includes reduced downtime, optimized throughput, and streamlined workflows.
- Facilitates Innovation: Reliable and predictable part dimensions enable engineers to design more complex and innovative products. Manufacturers can confidently push the boundaries of what’s possible without compromising on quality.
- Competitive Advantage: Companies that prioritize accuracy and precision gain a competitive edge in the market. They can offer superior products that meet stringent performance criteria, positioning themselves as industry leaders.
- Continuous Improvement: By monitoring accuracy and precision metrics, manufacturers can identify areas for improvement in processes, machinery calibration, and quality control measures. This continuous improvement cycle leads to ongoing enhancements in product quality and manufacturing efficiency.
Accuracy and precision in part production are foundational to achieving high-quality products, maintaining customer satisfaction, and driving operational excellence in manufacturing environments.
Experience Precision and Accuracy with BOYI Manufacturing Services
At BOYI, we specialize in delivering unparalleled precision and accuracy in CNC machining and plastic injection molding services. Our commitment to excellence ensures that every component we produce meets the highest standards of quality and reliability.
Why Choose BOYI?
- Advanced CNC Machining: Utilizing state-of-the-art CNC machines, we achieve precise and intricate designs with utmost accuracy. Whether you need prototypes or large-scale production runs, our CNC machining capabilities deliver results that exceed expectations.
- Expertise in Plastic Injection Molding: With years of expertise in plastic injection molding, BOYI transforms your designs into robust, high-quality plastic parts. From automotive components to consumer electronics, our molding process ensures consistency and durability in every product.
- Quality Assurance: We adhere to stringent quality control measures to guarantee that each part meets exact specifications. Our commitment to precision extends through every step of the manufacturing process, ensuring reliability and customer satisfaction.
- Custom Solutions: Whether you require custom prototypes or full-scale production, BOYI provides tailored solutions to meet your specific needs. Our team works closely with you to understand your requirements and deliver results that align with your vision.
Industries We Serve
BOYI serves a diverse range of industries, including automotive, aerospace, electronics, and more. Our dedication to precision machining and molding makes us a trusted partner for businesses seeking exceptional quality and performance.
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FAQ
The TV forecaster predicted a temperature range of 26°C to 31°C, which is a broad range and not very precise. The actual temperature at noon was 28°C, which falls within the predicted range, showing the prediction was accurate but not precise.
The oceanographer’s GPS and her colleagues’ GPS units all indicated they were at the correct location, showing precision because the readings were consistent with each other. However, they were all 50 meters off from the actual buoy location, demonstrating a lack of accuracy.
The colleagues’ weight estimates for the fish were 16.1 kg, 16.8 kg, and 15.9 kg. These estimates are close to each other, indicating high precision. However, the actual weight was 18.2 kg, meaning the estimates were not accurate.
In dart throwing, the bulls-eye is a fixed, visible target, making it easy to assess accuracy. Scientists measuring natural phenomena often lack a visible target or “true value” and must rely on standard references or averaged data to determine accuracy. Additionally, natural phenomena can vary and are not as predictable as a stationary target.
Yes, scientists can determine the accuracy of their measurements by comparing them against known standards, reference materials, or by using calibration tools. They can also use statistical methods to assess accuracy by comparing repeated measurements and calculating the deviation from the accepted true value.
Catalog: Blog
This article was written by engineers from the BOYI team. Fuquan Chen is a professional engineer and technical expert with 20 years of experience in rapid prototyping, mold manufacturing, and plastic injection molding.
