Calibration involves having devices (volt meters and current shunt/meters) tested on the bench against know reference standards.
Validation is usually a simple function check that is done more often, but lacks the certificates.
3.5 - verification
operations for the purpose of demonstrating that an item of welding equipment or a welding
system conforms to the operating parameters for that welding equipment or system
3.6 - calibration
set of operations which establishes, by reference to standards, the relationship which exists,
under specified conditions, between a DISPLAYED VALUE and a REFERENCE VALUE
[SOURCE: IEC 60050-311:2001, 311-01-09, modified – Notes removed and terms
"DISPLAYED VALUE" and "REFERENCE VALUE" used.]
3.7 - validation
operations for the purpose of demonstrating that a SET VALUE meets the REFERENCE VALUE
(within specified limits)
3.8 - consistency test
test to determine the repeatability of the equipment output over a period of time
Calibration
Set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material, and the corresponding values realised by standards
Validation
Confirmation through the provision of objective evidence that the requirements for a specific intended use (e.g. client specification) or application (e.g. product standard) have been fulfilled
You saved me the trouble of saying something similar but less precise and eloquent.
In my (way back) shop experience, auditors were unduly concerned about welding power source calibration. Voltage meters never go out of calibration and ammeters never stay in it (and are not very useful anyway).
"If you don't have time to do the job right the first time, when are you going to find time to repair it?"