Typically, a newly manufactured Geiger counter undergoes an "electronic" calibration at the factory, which comes with a Certificate of Conformance. But some customers will require or desire a N.I.S.T. calibration instead, which subjects the Geiger counter to an actual radioactive check source. The image above shows an example of a NIST Certificate of Calibration.
If you are purchasing an SEI brand of Geiger counter such as the Ranger, Ranger EXP, or Monitor 200, for instance, and want the NIST calibration when buying the unit new, then choose this option. This will add 7 to 14 days additional lead time to your order fulfillment.
Please note: This item applies only to NIST calibrations of newly manufactured SEI instruments, and not to periodic re-calibrations.