Measuring Instruments

Different types of measuring instruments are used in the laboratory to obtain measurements. Each of these devices contains a specific scale. Some volumetric measurements are used to obtain certain volumetric measurements. (Ex – Miter Ruler ). Other measuring instruments have a moving indicator ( Ex – Clock, Balance) Very accurate measurements cannot be obtained from any measuring instrument. This is due to some limitations associated with measuring instruments.

The smallest measurement of a measuring instrument

The smallest value that can be obtained from a measuring instrument is its smallest measurement.

Errors in a measuring instrument

  • The unavoidable error that can occur when making measurements using any aid is called the error or maximum error of that measuring instrument.
  • As a standard, this equates to the smallest measurement of the device.
  • Sometimes it is even considered half of the smallest measure.

Measure the length

  • The instrument used to measure the length is the meter controller and the international unit is m.
  • This is calibrated using millimeters and centimeters and the smallest measurement here is 1mm.
  • However, the steel rods used in the technology are also used to measure the length and its smallest measurement is 0.5mm.

Measurement with a meter ruler

Consider measuring the length of a microscopic slide.

Measuring Instruments
Meter Ruler
  • The smallest measurement of a meter ruler is 1 mm.
  • That is, the distance between two common markers is one millimeter.
  • The value of the mark that coincides with the left end of a slide is ‘0’.
  • The right corner is between ’41’ and ’42’.
  • That is, there is an error in the measurements obtained at this time.
  • That error is 1mm.
  • That is, the maximum error associated with a measuring instrument can be considered equal to its smallest measurement.

Fractional errors in a measuring instrument

  • Even if the error of a measuring instrument is a certain value, the effect of those measurements is different from the effect of the measurements obtained.
  • Ex – An error of 1mm is a significant value when measuring 2cm in length by a meter rule and is negligible when measuring a length of 200mm.
  • This effect is defined by the fractional error.
Measuring Instruments
Percentage errors equation

Percentage errors in a measuring instrument.

The fractional error is called the percentage error.

Measuring Instruments
Percentage errors equation

Accurate measurements on a measuring instrument.

If the percentage error of a measurement is 1% or less, that measurement is defined as a physically accurate measurement.

Sensitive measuring instruments

In some cases, approximate measurements in millimeters may not be sufficient. In such cases, work-sensitive equipment is used for the meter rule. Two principles are used in those devices.

01 – Vernier principle

i – vernier caliper

Vernier principle
Vernier principle

A vernier caliper is a common tool used in laboratories and industries to accurately determine the fraction of the minimum calculation.

The smallest measurement is 1 mm.

The vernier caliper is also useful for measuring the external and internal diameters of various objects.

It is also useful for measuring the depth of objects.

ii -Travelling Microscope

Travelling Microscope
Travelling Microscope

A traveling microscope is a device that measures lengths, usually with a sequential resolution.

It is designed to meet the needs of research, colleges, schools, and industrial laboratories.

Travelling Microscope uses a traveling microscope to accurately measure the diameter of various objects.

It is also used in physical laboratories, manometers, the refractive index of liquids as well as surface tension and viscosity tests to more accurately determine small variations in hydrodynamic levels.

02 – Screw principle

i – Micrometer screw gauge

how to use micrometer screw gauge.

Micrometer Screw Gauge
Micrometer Screw Gauge

A screw gauge consists of a ratchet, thimble, sleeve, spindle, and anvil.

Screw gauges are used to measure the diameter of ball bearings and wires, the thickness of the coin, and paper.

ii – Spherometer


A spherometer is an instrument used to accurately measure the radius of curvature of a sphere or curved surface.

Initially, these instruments were primarily used by opticians to measure the surface curve of a lens.

The vertical splits are on 1 mm, which is the pitch of the threads in the screws. The head of the screws is graduated to 100 degrees.

Since a sphere is essentially a type of micrometer, it can be used for purposes other than measuring the curve of a spherical surface.

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