[plankman]

The reference marker on some scales is located on the outside of the case and can consist of either a small round magnet (or it can be a small round steel insert) pressed into a hole near the travel position of the reader. The glass just has the serrations etched into the surface which the reader detects as it moves along the glass. There are a variety of means on Heidenhain scales. Usually the magnet is on mounted on the case, and the magnetic pickup is located in the reader. The telltale is a small cluster of fine chips if the machine is dirty.

The black strip you mentioned may have a hole or notch cut into the side of it which may also be the reference point. Try reinstalling the black strip in a different orientation, with the hole or notch located closest to the side of the reader, with the end of the strip with the notch or hole located at the end closest towards the home position. It may be there are a series of holes/notches along one side of the strip - try positioning this side closest towards the reader.

It's common for the z axis scale to have just one reference point, at the end furthest from the table so upon startup the machine will move away from the table. Then the y and x axes will move in a direction determined by parameter uintil they hit the next reference point. Typically Heidenhain scales have a reference every 100mm along the scale which is why the x and y axes don't go too far upon startup. Your machine may differ, however, so have a good look at that black strip!

Hope this helps, and good luck!