Working condition unknown, piece is sold as is with no returns. Other numbers I found were "5X". Please see the pictures posted and my store for many more great items. 

Another e-bayer had this to say: This item is a stereoscopic microscopic microscope.minus its pinion gear for the focusing mechanism. This scope was manufactured in Jena, Germany in the 1928-29 time period.This scope was sold by Carl Zeiss with two bases/stands and a single wooden oak case which accommodated both stands. One stand was large and suitable for use in a laboratory and included accessories for dissecting specimens for further examination. It have a large stage platform and oversized light reflecting double mirror. The other stand was much smaller for use in the field and did not have a stage platform or light reflecting mirror.. The item you have was used in either stand. I have the complete unit with the carrying case with serial number 20169