Pakistan study notes for Matric, Intermediate, B.A, B.COM BSC, M.A, BCS. Free Pakistani Urdu educational school, colleges and University notes.



An error is defined as,

“The difference between the measured value and actual value.”


If two persons use the same instrument, for the same measurement; it is not essential that they may get the same results. There may arise a difference between their measurements. This difference is referred to as an error.




Errors can be divided into three categories:

(1)       Personal Error

(2)       Systematic Error

(3)       Random Error


(1) Personal Error

An error comes Into play because of faulty procedure adopted by the

observer is called personal error.


Personal error comes into existence due to making an error in reading a scale.

(2) Systematic Error

The type of error arises due to defect in the measuring device is known as systematic error.


Generally it is called zero error. It may be positive or negative error.

Systematic error can be removed by correcting measurement device.


(3) Random Error

The error produced due to sudden change in experimental conditions is called random error.


It is an accidental error and is beyond the control of the person making measurement.

For example Sudden change in temperature, change in humidity, fluctuation in potential inference (voltage).



It is a defect in a measuring device (Vernier Callipers Screw Gauge).

When jaws of a Vernier Callipers or Screw Gauge are closed, zero of main scale must coincide with the zero of vernier scale or circular scale. If they do not coincide then it is said that a zero error is present in the instrument.

Types of Zero Error

Zero error may be of two types:

(1) Positive zero error

(2) Negative zero error


(1) Positive Zero Error

A positive zero error in the instrument shows a larger measurement than the actual measurement.

In order to get exact measurement positive zero error is subtracted from the total reading.

(2) Negative Zero Error

A negative zero error in the instrument shows a smaller measurement than the actual measurement.

In order to get exact measurement, negative zero error is added to the total reading.

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