Economy, interpretability and convenience are the three factors on which the practicality of a measuring instrument can depend upon. The measuring instrument should be practical from operational point of view.
The economic factor suggests that some form of trade off is required between the projects considered ideal and also which could be afforded.
Convenience test suggest that the measuring instrument should be easy for the purpose of administration. For the same, due attention should be given to the proper layout of the measuring instrument. For example: a questionnaire should have clear instructions to make it is easy to comprehend and complete it.
Interpretability is important as another important factor especially when persons other than the designers of the test are to be interpreted for results. In order to make the measuring instrument measurable for the purpose of interpreting it should be supplemented by detailed instructions for administering the test, for scoring keys and also to have evidence about reliability. It is also required as guide for taking help from the test and for interpreting results.