Mars Pro "Set Z Home" seemingly not working

[cliffyk]

I am not understanding something here.  Sorry for my failure in that.

If the set z=0 function is only to put it back into spec after long term printing, then it is correct NOT to do that unless all leveling practices fail to print.  Correct?

If that is true, then what does change the '0' position during the leveling?  If you go into the manual movement, perform the process (and in my non-surveyor definition of 'leveling' to make (a surface) level, even, or flat:, not the plane of the earth Surveying. to find the relative elevation of different points in (land), as with a level. for my definition please see 19, 20 and 27 here) then is it the most important part to go up 10mm 10 times?  Is that what the software/firmware calculates as the home position or z=0?  Where you stop then -100mm???

In the mechanical alignment process, initiated by loosening the lock screws and pressing the "home" button, the machine's "0" (furthest downward travel) position as determined by the limit switch does not change. What does change is that the physical position of the platen is changed to coincide with the limit switch "0" position.

Using the "Z=0" function establishes a logical "0" position , independent of the limit switch controlled "0" position. That logical "0" position is then used when G-Code Z-axis positioning commands are executed.

The go to "Home" positioning command will still send the Z-axis trolley to the limit switch controlled downward position. 

Thank you for helping me out here.

PS.  My first print failed miserably.  I saw metal shavings on the top of the build plate after tightening the screws.  Cleaned it off and didn't think much of it.  Machining aluminum isn't always perfect.  Well, when I went to unscrew the entire bolt it was cross threaded from the factory.  I have contacted Elegoo about this as they really should send me a new plate and screw, but if they don't then I just may return it to Amazon and go with a different brand.  I was able to get one of the spare screws (I see why they include them now  ) and it tightened down just fine.  I will need a new one if I start getting some prints.  As long as it works, I am fine with buying new parts for it as this was partially my fault for following the directions...