It is extremely vital to check the zero setting after checking the caliper jaws for wear. This process is obvious: close the jaws and check if the vernier reads 0.000. Then, you can adjust to zero by loosening the adjusting screws, and repositioning the adjusting screws, and repositioning. For reliable measurement, this process might not provide the best solution. If most of your measurements are in the 75 to 130 mm (3 to 5in.) range, for example, you should zero at the 100mm (4 in.) point—the approximate center of where the majority of your measurements on a standard of known size (true value) such as a gage block.
Here, we have summarized some information about vernier calipers, but without making any allowance for good or bad manipulation. We will include a table like this one for each important instrument, because the table will help you select the best instrument for the job, whether in the physics laboratory or in the shop floor.