Physics 2. In certain activities, a single measurement is sufficient. However, in many activities the reliability of a single measurement is low compared to a set of measurements made under the same conditions. It is often preferable to take several measurements and use the average of these readings when analyzing the results. 3. Personal error can arise from personal bias or carelessness in reading an instrument, in recording observations, or in mathematical caloulations A. For example, in performing a series of measurements, a student may become biased in favor of the first observation. Falsely assuming this observation to be correct, the student attempts to make other measurements agree with the first. This incorrectly gives more significance to one reading than to succeeding ones. All observations taken under the same experimental conditions are equally valid and should be retained for analysis. B. Reading a value from a scale involves lining up an object with the marks on the scale. The apparent distance between two objects, and hence the value of the reading, depends on the position of the eye. A reading may appear to be different when viewed with one eye or the other, or when the head is moved from side to side or up and down. This apparent measurement difference is due to a change in position of the observer, and is called parallax. It is important to note that most students incorrectly use a metrio ruler or meter stick by placing it flat against the object. The thickness of the ruler or meter stick holds the scale about 0.7 om from the object, causing readings to vary due to parallax. You can minimize such error by placing the ruler or meter stick so that the edge is against the object. You now can have a line of sight perpendioular to the scale. This is so logical, but most of us were never taught this little tip. C. Oooasionally, students measure correctly, but simply write down the wrong number(s). It is so easy to transpose numbers or incorrectly enter numbers into a oaloulator. Always check your numbers before proceeding with the activity. 4. Choose the instrument that is best suited for the required measurement. For example, suppose you wanted to measure the thickness of a dime. You might attempt the measurement with a metric ruler, but due to the small size of the dime, the value would be suspicious. A vernier caliper would be a better choice for the measurement. The caliper yields a more reliable measurement in this situation. 5. Due to the size of an object (very small or very large), it may be difficult or impossible to make a direct measurement. An alternative method known as indirect measurement may be utilized. In this process, other measurements are taken, caloulations are performed, and a reliable estimate for the needed value is obtained