What is a working standard?
A working standard, also known as an in-house standard or secondary standard, is an alternative to a certified reference material provided by reference material manufacturers. The working standard is used for instrument calibration, performance verification, repeatability and reproducibility test, accuracy test, and demonstration. Compared to certified reference materials, working standards are much more cost-effective but probably cannot provide the same level of accuracy.
However, these working standards are also easier to produce and meet the ISO requirement.