What about measurement? To position any device precisely, you could try counting steps or use a digital caliper. But there is a cheaper way, awire. At 100 Ohms per meter, this can be attached directly to the AD-converter of the µC. But the current must be limited and hence the accuracy is slightly reduced. The result is still good enough for simple tasks.

In the picture you see the wire (or not) attached to the fixed mount on the left. Above it the contact spring, attached to the Z-slider. The red wire is attached to the contact. The yellow wires are attached to the endpoints of the resistance wire. In the next picture you see the contact spring in close up. Here, you can see the resistance wire, too:

The isolation of the wire was removed by a razor blade.

The precision of this can be seen in the videos.  

big:  

small:

Frankly, it can be used for  a rough absolute positioning. In the first video, it's a automatic drive between positions 720 to 734. In the second it's a smaller distance to show the wiggle at the endpositions. The reasons are inacuracies in the whole setup, mainly the wire itself. The price for the wire: 2 EUR. It would last for 25 axis or 8,3 Shelfies. I doubt, it can be beaten.

Regards!