Jason,

I believe Zeiss uses "Microns per millimeter" to calculate thermal expansion.
You should be able to convert the numbers from the Machinist Handbook for you material.
ie, Aluminum is 23.1 microns per millimeter (0.0231 mm)

You should consider posting this same question on the Zeiss Web site at
www.zeiss.com/imt and look under forum.

Hope this helps.

John