A. Standard Equipment (Primary)
If there is any standard equipment or equipment then it should be a reference primer is used to check the calibration of equipment. NIST (National Institute of Standards and Technology) in this respect and who has the authority to always maintain and provide standards that are required in measurements, eg temperature, mass, and time.
B. Secondary Equipment
Usually when the primary standard can not be found it can use a secondary standard measuring devices other form that is believed to have better accuracy. For example, a voltmeter when used show a reading of 4.5 volts. Another tool that is believed accuracy (secondary standards) yields a value of 4.4 volts. By this means the voltmeter can be calibrated smaller 0.1 volt.
C. Precision
A measuring instrument for the measurement is said to be precise if a certain physical quantity that is repeated then the measuring instrument is capable of producing the same results as the previous measure. For example if the measuring voltage with a voltmeter generate measurement is repeated several times and then still produce a reading of 5.61 volts, these tools are very precise. Therefore, the precise nature of a measure depends on the resolution and stability of the measuring instrument.
D. Resolution
A measuring instrument is said to have a high resolution / good if it is capable of measuring changes in the value of physical quantities on the scale of change that is getting smaller. I smallest scale voltmeter with mV certainly has a better resolution than the smallest reading voltmeter with a scale of 1 volt.
E. Stability
Stability measuring instrument associated with the stability of the measuring results / readings are free from the influence of random variation. So, is associated with the appointment of the reading results did not change during the measurement. Voltmeter needle is not moving to the left or to the right around a certain value. So, a good measurement tool must have good accuracy also need to produce high precision. A measuring instrument may only have good precision, but not accurate, and vice versa. In addition to a measuring instrument needs to have good accuracy and precision, it is also necessary to have high sensitivity.
F. Sensitivity
If the measuring instrument has a good response to small changes signal input / input so that the output (read) to follow these changes then the device is said to be sensitive.