Yes this is another Dial Indicator Holder, but this one is different! I tried one of the others, and found the whole approach rather silly - why sit the indicator holder on the gantry rails when you can clip it onto the extruder and use the jog controls in ReplicatorG to position it?
With this clip-on dial indicator holder you will get repeatable results, because you are relying on the extruder rail bushes to position the dial indicator over the levelling screws on the build plate.
UPDATE (13 Feb 2013)
There are two new STEP files which can be imported into other CAD programs. The first can be customised with your own hole size to suit different types of indicators. The other is a blank holder that can be used to design your own attachments.
There is also a new script that automates the process so you don't even have to use ReplicatorG any more to control the process. The gcode has been exported as an x3g file - ready to download to your printer's SD card.
This indicator holder was designed using an ACIS solid in Shark FX (sfx file included) so will behave well with Makerware, ReplicatorG and skeinforge.
Because a few of you have asked - Paypal donations graciously accepted - whpthomas at yahoo dot com