It's possible that you're referring to:

* Optical Displacement Measurement Equipment (ODME): This is a broad term and could refer to many different types of instruments. Calibration media would depend on the specific type of ODME being used.

* Optical Distance Measuring Equipment (ODME): This is another potential interpretation. Again, the calibration medium would depend on the specific instrument.

To provide a helpful answer, please provide more details about the specific type of ODME you are referring to.

For example:

* What is the purpose of the ODME?

* What type of measurement does it perform? (distance, displacement, etc.)

* What is the brand and model of the ODME?

Once I have more information, I can give you a more specific answer about the calibration medium used.