What is measurement?

Measurement is about determining the quantifiable attributes of a target object. Examples of these attributes include:

• length
• weight
• distance
• thickness
• position
• capacity
• size

The following sections explain more about what measurement is – and isn’t.

Why is measurement misunderstood?

Sometimes, people use the term “measure” instead of “calculate” or “quantify”. All these terms are related, but they’re not the same. For clarity’s sake, think of measurement as a single action that you perform with instrumentation. Collectively, “instrumentation” describes devices (i.e., instruments) that measure, indicate, and sometimes record values.

Today, there are many different types of specialized measuring instruments. Bakers use different measurement tools than electricians, and both use different measuring systems than carpenters. For the purposes of this article, measurement is understood to be used with the design, inspection, and production of manufactured products.

What’s the difference between inspection and measurement?

Inspection is about determining a physical attribute (e.g., size) and comparing it to a reference standard to decide whether the measured object is close enough to the standard to be acceptable. Measurement is about finding or determining this physical attribute, but not necessarily about comparing it to a standard or making a decision about the product’s acceptability.

Here’s another way to understand the difference. When you’re using a ruler to measure an object’s length, you might say that the measurement is either too long or too short. You probably wouldn’t say that based on the value from the ruler, the measurement obtained is either longer or shorter than the desired measurement. The first statement is far simpler, of course, and it’s also generally understood.

What are the two types of measuring systems?

There are two main types of measuring systems: direct and indirect.

Direct measurement systems do not translate what is measured into some other characteristic. Simply put, they directly measure what you want to know. Examples include measuring your height with a measuring tape, determining the temperature of your oven with a thermometer, or measuring the speed of your morning run with a stopwatch.

Indirect measurement translates what is measured into another characteristic. It’s less common in daily life, but important in manufacturing. For example, Accumeasure technology measures capacitance, the ratio of the change in an electric charge to the corresponding change in its electrical potential (i.e., voltage),  in order to determine the distance between a probe and target.

 

Inline/Offline Measurement

Inline and offline measurements refer to two different types of measurements. Inline Measurements are commonly referred to as automatic measurements made during a process . Offline measurements, on the other hand, are often referred to as manual measurements. The difference between the two occurs during the measurement process (line). If the measurements are included in the line then the process is considered “inline”. If it’s separate from the line then it’s considered “offline”. For off line measurements products are removed from production , inspected and returned to production ,discarded or saved as inspection samples

Inline Measurement

An Inline Measurement suggests that instruments or sensors are situated in a flow-through system. An excellent example would be a sensor attached to a manufacturing line that continually monitors the products that pass underneath. While scanning, the system should be able to ascertain the following information:

• Able to register the shapes and dimensions when judging the acceptability of a product.
• Able to perform measurements when a product passes underneath the sensor.
• Able to make a proper judgment when determining the acceptability.
• Output of NG judgment when a product has not been accepted

Inline measurement that occurs without the skill of an operator can be repeated for a large amount of products. When humans are thrown into the mix the question of skill always becomes an issue. However, when the process becomes automated there are less chances that mistakes will be made. Furthermore, consistent automated monitoring helps to identify when unacceptable products appear. This helps when tracking traceability.

In the production world work conditions can be quite demanding. Measurement results play a central role. Precision is key. Finding undesirable products on a line can only work if the tolerance testing during the production process is precise enough to reliably sort out all of the products that deemed to fall under tolerance levels.

Inline systems should be accurate no matter what type of work environment it’s in. For example, an inline measurement should be precise even if a temperature drift were to occur. Temperature drift can be caused by the surrounding temperature itself, such as the temperature in the warehouse where the inline system is located, or by the board itself. To ensure that temperature drift is not an issue, it would be a good idea to only use high quality components on your system. Also, you should pay close attention to the layout of the board. For example, components that are known to heat up while in use should be placed in an area where they will not heat up the other components of the system unnecessarily.

Also keep in mind that a good inline system can maintain its precision through interference resistance. All types of interferences can occur in the workplace:

• Mechanical – shock, vibration
• Climatic – chemicals, oil, lubricants, water, temperature, humidity
• Electromagnetic – short-circuits, ground loops, EMC radiation, overvoltage, current peaks

Ultimately, when using inline measurement, precision through automation is key no matter the conditions of the workplace.

Offline Measurement

Offline measurement relies completely on the human element. Offline measurement occurs when a measurement is performed by manually handling the measurement system in order to attain measurements for any given point or object.

Where Inline Measurement relies upon the automation and precision of machines, Offline Measurement relies upon the skill of an operator. Measurements can vary depending upon the skill of the operator. Due to the human element, offline measurements are typically not as precise as inline measurements (once again this depends upon the skill of the operator). Furthermore, due to the fact that constant monitoring is not performed, it can be quite difficult to track when unacceptable products began to appear due to a lack of statistical data. Establishing a consistent schedule of accurate measurements is considered to be an important factor in discovering stable test results.

 

Tolerance

Tolerance refers to the total allowable error within an item and is specifically represented with the symbol +/-. During the manufacturing process it’s almost inevitable that items on the line can become damaged at one point or another. Products can face damage in multiple ways. For instance, changes in temperature and humidity can cause a product to become warped and disfigured. Warping can also occur if there’s improper feedback from the process control device. No matter the reason, it has become necessary to take any and all errors into consideration during the manufacturing and inspection processes. When used in this manner, tolerance is factored into the equation when the acceptable error range (the range where the quality of the product in question is still intact) is being set. The assumption is that a variation can occur at any given step during the manufacturing process.

Measurement Accuracy

Accuracy refers to a measurement’s degree of correctness. When this process is applied to the measurement process, it becomes known as measurement accuracy. Measurement accuracy becomes vital when attempting to ascertain how accurate a result will be. Measurement systems that have a greater measurement of accuracy are capable of performing more accurate measurements.

What Is a Measurement Error?

A measurement error is the difference between a measured value and the true value of the quantity being measured. This can occur due to imperfections in instruments, environmental conditions, or even human mistakes. In short, errors in measurement reflect limitations in the measuring system.

There are three main types of errors in measurement:

1. Gross Errors: These are usually caused by human mistakes, such as recording a wrong value or reading an instrument incorrectly. For example, misreading a scale or using the wrong measuring technique results in a gross error.
2. Systematic Errors: These are repeatable errors that occur due to flaws in the measurement system, such as instrument calibration issues or environmental factors like temperature or humidity. A systematic measurement error skews results in one direction consistently.
3. Random Errors: These are unpredictable and occur due to unknown or variable influences, such as small fluctuations in the environment or limitations in observation. An example of random error might be slight variations in a digital reading each time you measure the same object.

Examples of Measurement Error

• A scale error in measurement may happen if the measuring scale itself is miscalibrated.
• Human error in measurement includes parallax errors, misreading instruments, or data entry mistakes.
• Instrumental errors come from worn-out, poorly maintained, or incorrectly calibrated instruments.
• A gross error example is when a technician writes “16.3 mm” instead of “13.6 mm.”

What Causes Measurement Errors?

Measurement errors can result from:

• Personal errors – mistakes by the person performing the measurement.
• Instrumental errors – due to faulty or poorly calibrated equipment.
• Environmental errors – changes in temperature, humidity, or pressure.
• Observational errors – limitations in the observer’s ability to read instruments accurately.

How to Reduce Errors in Measurement

To reduce measurement errors:

• Calibrate instruments regularly.
• Train personnel to minimize human error.
• Use more precise measuring tools.
• Control environmental variables when possible.

Error in Measurement Definition and Importance

In science and engineering, errors in measurement aren’t just mistakes—they represent the uncertainty associated with any measurement activity. Recognizing and classifying them helps in making informed decisions and ensuring the safety and accuracy of products.

Understanding measurement errors is essential for achieving reliable and accurate results in science, engineering, and quality control. By identifying the types of errors in measurement—gross, systematic, and random—you can trace the sources of measurement errors and apply corrective actions. Whether the issue is due to faulty instruments, environmental conditions, or human error in measurement, knowing how to detect and reduce these errors helps ensure consistency and confidence in your data.

 

Reference : Vitrek LLC