Explanation Accuracy is the closeness of a measured value to the true value. The difference between the measured values from the true value has been defined as the error. Therefore, the accuracy of measurement with a given instrument is high if the error in measurement is low and vice versa. The accuracy of an instrument can be determined by taking repeated measurements with the same instrument and taking the average of the measured values. If the difference between the average value and the true value differ by large amount, the instrument is less accurate and vice versa. The precision of an instrument can be determined by repeated measurements of the same quantity with the same instrument. The precision of an instrument can be analysed by finding the difference between the highest reading and the lowest reading. If the difference is less it can be said the instrument is precise. On the other hand, if the difference is large it is less precise. In other words, if the readings are close to one another the instrument is more precise and if the readings are scattered or deviate too much from one another the instrument is said to be less precise. Precision is a characteristic of an instrument that gives a consistent performance, and the number of decimal places to which a measurement can made indicates the precision of the instrument used. The difference between accuracy and precision can be understood by considering the following example. Four vernier calipers, A, B, C and D are made by four different manufacturers. It is required to compare the accuracy and precision of these four instruments relative to each other. It may be noted that it is possible that a given instrument can be either, accurate as well as precise, less accurate and more precise, more accurate and less precise less accurate and less precise. Suppose, the length of an object is correctly known previously as 4.08 cm. Now, the same object is measured with the four different vernier calipers and six measurements are made with each instrument and the observed reading is given in the following table. Procedure: First, compare the average values for the calipers A and B. We find the average value of A is more close to the true value compared to that of B. Therefore, it can be said that Calipers A is more accurate than B. Now let us compare the scatter in the values or the difference between the maximum reading and the minimum reading. The difference is less in the case of B compared to A. Therefore, caliper B is more precise compared to A. Likewise, we can compare both accuracy and precision between any two instruments. The following points highlight the major differences between the terms accuracy and precision: ACCURACY PRECISION Accuracy expresses the closeness of the measurement with the true value. Precision expresses the 'closeness' of the repeated measurements to each other in the experiment. Accuracy depends on instrument and human errors. Precision depends on random errors, which are unpredictable. Smaller the error, higher is the accuracy and vice versa. The number of decimal places indicate how precisely a measurement has been made. Accuracy can be improved by re-calibration of the instrument or by reducing human errors. Precision cannot be improved.