Calipers are a common and useful length measurement instrument. More accurate than a ruler and hardier than a micrometer, they are found in many engineering environments. When looking at a caliper, it's quite apparent that the large jaws can be used for external measurements. However, many users don't realize that calipers can be used to make a range of other measurements like internal measurements, depth measurements and even step measurements.

In this short article, we wanted to showcase the four main types of measurements that a caliper has been designed to take.

External Measurements

External measurements are taken using the external jaws, highlighted in figure Z.

Figure Z

Some examples of external measurements are shown in figures X, Y, and W below.

Figure X
Figure Y
caliper measurement
Figure W

In Figure X, a small measurement is being taken on a In Figure Y, a medium measurement is being taken on a In Figure W, a large measurement is being taken on a External measurements may be the most common type of measurement taken using a pair of calipers.

Internal Measurements

Internal measurements are taken using the internal jaws on the 'back' of the caliper, highlighted in figure V.

Figure V
Figure T
Figure R
Figure Q

In Figure T a small measurement is being taken on a When taking small measurements on cylindrical objects, an error can be introduced commonly called "Cross knife error". This error can occur when the flat of the jaws is not fully in contact with the target surface being measured. Figure S is a technical diagram from a standard for the calibration of calipers - ISO 13385-1:2019 demonstrating this error. Figure R a medium measurement is being taken on a Figure Q a large measurement is being taken on a

Depth Measurements

Depth measurements are taken on a caliper using the depth measurement rod, highlighted in figure P.

Figure P
Figure O
Figure N
Figure M

The face you use to rest on the surface being measured is narrow and small, making it easy to angle the caliper away from the dimension you're aiming to measure. This can introduce errors to a measurement, as visualized in Figure O. Figures N and M demonstrate some depth measurements being taken. Depth rods are especially useful for measuring the depths of tapped holes. If you find yourself often taking depth measurements, CCS sells a device that provides a larger base from which to stabilise the caliper. This can make taking depth measurements easier and reduce the possibility of measurement error. Please see this item [hyperlink] in our shop for more information.

Step Measurements

Step measurements are taken using the step ledge located on the back of the caliper, highlighted in figure L.

Figure L
Figure J
Figure I

Step measurements are useful when measuring a "ledge" on an object. When both jaws of the caliper can't fit inside or around the object, the step ledge is the way to go. Figure J shows an object that can only be measured using the step ledge. Figure I shows another obejct that can only be measured using the step ledge. Calipers are an extremely useful instrument for many kinds of length measurments. Depending on the quality of build, they typically have accuracies less than 0.04mm. Their ability to measure many different types of dimensions in a single insturment is unique amongst measuremnet equipment. They fill a very ipmortant role in any machine shop, testing laboratory or workshop. To purchase a calibrated caliper, please visit our curated shop [link]. We only stock items that are of high quality, though we do sell a range of brands - some well-known and others less common in this market. We offer traceable calibrations on calipers, which meet the calibration requirements of the general public. We also sell calipers with a NATA accredited calibration (ISO 17025), which meet the requirements of organisations that maintain a quality system. If more accuracy is required than a caliper, one could use a micrometer, though micrometers typically only perform external measurements. If less accuracy is needed, one could use a ruler or tape measure.

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