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Once I installed the gas spring and removed the old torsion spring, installing the Z axis DRO was super easy. I removed the ruler on the left side of the column a while ago, since it was so course it was pretty much useless. The 12" iGaging digital scale was the perfect length to screw right into the holes left by the ruler. I then quickly fabricated a bracket to connect the scale's reader to the threaded hole on the head which used to hold the ruler's indicator. Perfect.
With the addition of the this last digital scale I now have one installed on all three axes. Further down the road I really want to eventually convert the scales from using their individual displays to using an Android tablet as a DRO with this: