1) Accuracy of the electronic module
Digital caliper’s accuracy is dependent on the quality and accuracy of the components or mechanical parts, the stator strip sensor, and the electronic module. The manufacturing process of the electronic module requires advanced technology and equipments that are high precision. Mostly, in China, are found several industries which manufacture the said electronic modules for digital calipers. However, there is only one manufacturer of this electronic module which can produce such with high accuracy. Low end electronic digital calipers with low-cost and low-quality electronic modules produces low accuracy in measurement. In purchasing a high quality digital caliper with highly accurate electronic module, one must consider the device itself and make sure that it has a set of nine- (9-) piece gauge blocks with step increments of 0.5 millimeter, such as 1.00, 1.50, 2.00, 2.50, 3.00, 3.50, 4.00, 4.50, and 5.00 millimeter or that with a module master.
2) Accuracy of the outside measurement
Inspect the inside measurement of a digital caliper using a gauge block set or a step gauge. An equivalent of plus/minus 0.02 millimeter (or equal to 0-100mm) and plus/minus 0.03 millimeter (or greater than 100mm to 300mm), shows that the accuracy is within the prescribed range of the National Standard.
3) Clearance of the closed measuring faces
Another thing to consider is the clearance of the closed measuring faces. This can be done through some simple and easy steps. First, close the measuring faces and hold the device between your eyes and against the light. Align these: light, measuring faces, and your eyes. The measuring faces are well lapped if light can be seen from the closed measuring faces. A high quality digital caliper has well lapped measuring faces.
4) Type of stator strip sensor
What can the stator strip sensor say about the quality of digital calipers? Low end digital calipers employ stator strip sensor which is made of copper plating glass-epoxy lamination. On the other hand, high-end digital calipers employ stator strip sensor which is made of indium coated glass. The glass sensor coated with indium is far more reliable than that of copper plating glass-epoxy laminated sensor. Another advantage is that the former has relatively smaller coefficient as compared to that of the latter.
5) Bar Parallelism
What is bar parallelism and how can the same be a factor in choosing the better, and accurate digital caliper? Here are some helpful procedures. First, close the jaws of the digital caliper and slightly lock the slide using the lock screw. Then slowly pull the slide all the way through the end of the whole bar and notice if it can move freely all throughout. If it does, then this is a good indication that the bar parallelism is superior. If it does not move anywhere farther from the origin, then it is an indication of poor bar parallelism. Bar parallelism affects the accuracy of the digital caliper, and a superior or poor bar parallelism as can be determined by the aforesaid procedure is determinative of the accuracy of the device.