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## Units

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**Units**• Definition: The standard measure of each kind of physical quantity is called a UNIT. • Measurement: Measurement implies comparison with a standard value. The magnitude of a physical quantity can be written as: Numerical ratio x Units**Types of Units**• In Science and Engineering there are tow kinds of Units: • Fundamental Units • Derived Units • Units to measure Length, Mass and Time are known as Fundamental Units. • All other units which can be expr3esseed in terms the fundamental units are called Derived Units.**Dimension**• Definition: • The unique quality of every quantity which distinguishes it from all other quantities is called dimension. • Dimensional symbols for Length, Mass and Time are: • L, M, T • All Derived units would be defined as multiple of fundamental dimensions: • Volume….L3 • Speed …..LT-1 • Acceleration …..LT-2**System of Units**• British System of units describes fundamental in centimeter, grams and seconds and therefore called CGS system. • The System that uses Meter , Kilogram and Second is called MKS. • International System of Units…SI mostly uses MKS units but is rationalized in application.**Types of SI**• SI units are divided into Three: • Base Units • Derived Units • Supplementary Units**Definition related to Instruments**• True or actual Value: That magnitude to measuring system which can be approached and never evaluated is termed as True Value. • Indicated Value: The value which is indicated by the instrument. • Correction: The revision applied to the critical value so that the final result obtained improves the worth of result is called correction. • Overall error: The difference of sacle reading and true value. • Range: The region between the limits an instrument can operate.**Definition related to Instruments**• Sensitivity: The ratio of output response to a specified change in the output is called sensitivity. • Minimum measurable change in variable is called Resolution sensitivity. • Lowest level of measured variable that produces effective response is called Threshold sensitivity. • Scale Sensitivity: The ratio of change in scale to corresponding change in pointer deflection. • Scale Readability: