What could contribute to an inaccurate vital sign reading?

Lack of training in getting the vital sign or worst, not knowing the right way to take the vital sign could contribute to an inaccurate vital sign reading. For example, if you are tasked to get the respiration of the patient, the rule is to count inhale and exhale as one. But if you were not able to know this rule, and you counted inhale as one and exhale as another, this could impair the vital reading.