1) Accuracy: The degree of exactness (closeness) of a measurement compared to the expected (desired) value.
Closeness with which the instrument reading approaches the true value of the quantity being measured is known as accuracy
2) Precision: It is the measure of consistency or reproducibility of measurements. OR The closeness with which the individual measurements are departed or distributed about the average of number of measured value.
3) Measurement uncertainty: it is the parameter, associated with the result of a measurement that characterizes the dispersion of the values that could be attributed to the measured. It is the standard deviation of the probability distribution over the possible values that could be attributed to a measured quantity
4) Tolerance: Ability of an item or system to withstand high levels of stress or overloading without suffering irreparable harm.
The difference between standard instrument reading and measuring instrument reading is known as error and if this error is permissible then it is called as tolerance OR Allowable variation in actual measured value and desire value