Firstly, a probe must be as short as possible. As usual, it is easy for a long probe to bend and deflect, which will affect the accuracy of test. So we need to choose a short probe in order to avoid the above situation and ensure great accuracy of test.
Secondly, it is best to have fewest junctures. When a probe is applied, it needs to be connected with a lengthening bar. However, it is easiest for a juncture to bend and become deformed. A juncture just means choosing a long probe, bending or deformation of which will affect the accuracy of a probe or even make a probe unable to carry out the test correctly. Thus it is necessary to avoid junctures.
Thirdly, measuring balls need to be as big as possible. The bigger a measuring ball is, the wider the gap between cues becomes. A wide gap will reduce the possibility of triggering caused by the swing. When the diameter of a ball is large enough, the effect of unpolished tested surface on test accuracy could be weakened.
The above are general principles summarized for you to select a proper probe. A probe with high accuracy could be chosen following these principles. When accuracy is greater, test values will be more ideal. Ideal values could help you get desirable results in your work.