What is the difference between calibration, verification, Qualification and validation?

Calibration :

• The act of checking or adjusting (by comparison with a standard) the accuracy of a quantitative measuring instrument.
• Calibration can be considered as a comparison between two entities, to ensure one is equal to the other, within the accepted tolerances. The entity used as a reference in the comparison is known as the standard.
• Ensure the measurements accuracy of an instrument compared to an known standard.
• Comparing against a reference standard.
• Calibration is identifying and adjusting  when possibles the measurement errors of a measuring.
• Reference standard (Known standard) used in calibration.
  

        Verification:

• Checking standard process.
• Reviewing, inspection or testing the process.
• Ensure the correct operation of equipment  or a process according to its  stated operating specification.

Validation:

• Documenting that a process or system meets its predetermined specification and quality attributes.
• Ensure that a system satisfies the stated functional intent of the system.
• No reference standard are required in validation programme.
• Validation provides documented evidence that a process,equipment  method or system produces consistent results.

Qualification:

• System and equipment are properly installed, and work correctly and lead  to the expected results.
• Qualification is the part of validation (the initial stage) of validation.