Cheap DRO system using digital scales and a PC

Hello Members of this group,

Recently I obtained two damaged linear scales, which I got working
again. However I want to construct a cheap DRO system out of them,
and I need some info on this.

The scales are probably working with the capacity principle, similar
to the Mitutoyo (and other) digital calipers. They have a sliding
head with all the electronics in them and a small display, driven by
an SR44 battery, working with an accuracy of 0.01 mm, which is good
enough for me. I know they would give me a fast and extremely
accurate DRO system, but it will probably be good enough!

Questions:
1) Each of the scales is having a possibility for a data connector,
with 4 wires. However I can not determine the type of connector
needed. Any suggestions? It looks like a small flat connector with 4
wires on a 0.1" grid.

2) I need a designation of the 4 connections, which one is ground,
clock, signal etc. and what is the protocol typically used on these
scales. I have read that this is often an SPC interface, but I am
unable to find the specification for this SPC. Any pointers??

3) I want to hook up 3 or 4 of these scales on my lathe or mill, and
connect them to a PC, and write some software to display the data. Is
anyone havng a pointer how to connect these scales to either the
serial or parallel port. Do I need some electronic in between to
convert voltage levels, or to provide some opto-isolation? If the
serial port is used, how canI hook up multiple scales through 1 port ?

Making some electronics should not be to difficult for me, writing
the software is my profession, so that should be ok as well.

Thanks for your suggestions,
Frans Nieuwerth, the Netherlands.