This is the Leak Standard that you use to verify your refrigerant leak detector is working properly and is properly calibrated.  From Yellow Jacket products division of Ritchie Engineering Company.  A must for maintaining your HVAC Leak Detection equipment.

This Yellow Jacket Refrigerant Leak Standard Test Vial 400374 is the ultimate solution for HVAC and refrigeration professionals who want to detect leaks with ease. With its high-quality design and precision technology, this leak detector reference standard from YELLOW JACKET is a must-have in your toolkit.