Measuring Devices, Measuring Tools, Calipers, Goniometers

What is a Caliper?

A caliper is a measuring tool that determines the length or width of an item by fitting it between the two prongs or arms on the device. To permit adjustment of the gap, at least one of the arms moves until it fits the measured item exactly. Variations of this device include thickness, dial, and Vernier calipers. The typical structure of a caliper is an “L” shape, and the shorter arm of the “L” of the caliper is fixed in position. The other caliper arm slides back and forth along the long side to allow precise fitting of the arm around the item being measured. Beginning with the zero where the two calipers meet when the gap is closed, the incremental distances are marked on the long side of the “L.” Calipers can also be fitted with an attached dial or digital readout to show the results.

The tips on a caliper can have different shapes. For example, some can come to a conical point for an exact measurement at the ends. Others have pointed tips which have flat interior sides to fit snugly against an item’s surface. Tips can also bend inward 90 degrees to accommodate a threaded or grooved surface. A dial caliper is specifically made for internal pipe or cylinder measurements. Two bent prongs are put into the cylinder and spread using a spring loaded adjustment until the prongs touch the insides of the cylinder. To ensure accuracy, the dial display has a bezel which is zeroed before the measurement is taken. Some “L” shape calipers are made with bent prongs on the opposite side from the regular calipers so they can measure an internal diameter.

Vernier calipers add an extra measuring gradient to the standard “L” shape caliper. A Vernier scale uses a measure of 90% of the standard scale to provide an exact reading for one additional decimal place. This type is used when precision is critical. Sometimes it is necessary to measure the thickness of a person’s skin with a modification of a caliper called a thickness gauge. From a handle on one end, two arms extend to the side or directly from the end with rounded or flat spring loaded tips which point to each other at 90 degree angles. The arms are slipped over the skin or other item to be measured, and the gauge reads the thickness of the skin or item that is between the arms of the calipers.

What is a Goniometer?

A goniometer is basically a device that is used in angle measurement. Various types of the goniometer are used in a number of different fields, including physical therapy. While measurement normally involves calculating the dimensions of an object, there are also other forms of measurement that are used in a variety of applications. A goniometer is a helpful device in many of these tasks. It is ideal for use in the fields of occupational therapy and physical therapy because angle measurements are the key function of the goniometer. There is a need to measure the range of motion that is associated with various muscle groups and joints in both fields. For example, it may be used to help determine the current ability of the range of motion in bending the knee, bending the arm at the elbow, or bending at the waist. The device can help establish the range of motion at the beginning of a treatment series, and help allow the therapist to monitor an individual’s progress during following sessions.

What is a Spirometer?

A spirometer is a device that is used to measure the flow of an individual’s breath in and out of the lungs. It is used in a medical testing procedure known as spirometry. This is where a patient breathes in and out of a tube which is connected to the spirometer so lung function can be evaluated. A spirometer produces a graphical output, with the time along one axis and the airflow along another. This enables a doctor to see how much air the patient is breathing in and out as well as the period of time that is covered. By looking for the high point on the graph, a peak flow value can also be obtained.

It takes some practice to learn how to work a spirometer. At least three cycles of breathing are done on the spirometer to get a range of values which can be averaged to show the patient’s condition. If the numbers are widely different, it may be a sign that one or more of the tests was incorrect and should be repeated. Spirometry is highly dependent on patient cooperation. It is important to remember it does not measure total lung volume, but only the amount of air that can be pushed in and out of the lungs. For example, someone with severe bronchial obstruction may have a very high lung volume, but this would not be shown in a spirometry test because only a limited amount of air could be forced through the bronchial tubes.

What is a Volumeter?

A volumeter is a device used to measure volume, the amount of space an object takes up in three dimensions. It has a variety of applications, ranging from research labs to medical settings. A container filled with water is one of the oldest and simplest example of a volumeter. The volume of the object can be measured by determining how much water is displaced when it is placed in the container. Other volumeters may rely on displacement of other substances, such as gases or solids, depending on what is being measured. Solids, liquids, and gases can all be measured in a volumeter, and it is possible to collect specific gravity information as well.

Since a volumeter is a sensitive device, it may need to be calibrated before using it and periodically to confirm it is still as sensitive as needed. To avoid damage or breakage that may interfere with the integrity of its measurements, a volumeter should be handled carefully. Some can come with calibration tools like premeasured blocks to make sure it is performing accurately.

Rehabmart is pleased to carry a wide variety of professional measuring devices from renowned medical vendors that include Fabrication Enterprises, Sammons Preston, Chattanooga, North Coast and Medline.

Hulet Smith, OT
Rehabmart Co-Founder & CEO

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