Why is Z = 0 not = table?

[mawa]

Trying to test Z axis preset value like table, PCB, Focus I came to the question why the LitePlacer homes Z at the top most position and not at the table level?

As most Z measures are relative to the table e.g.
PCB Height = Table height(0) + PCB Thickness,
Tape Pickup height = Table Height(0) + Tape Component Height,
Placement Height = PCB Height + Component height + Paste Height (to prevent squeezing away all solder paste between the PCB and the component)

Is there a specific reason why the axis is kind of upside down?

After a needle change a recalibration = Home Z is IMO always necessary to get the true needle length.

[JuKu]

> why the LitePlacer homes Z at the top most position?

To get a consistent position reference that is available no matter where the machine is, what happens to be under the needle or even when there is no needle at all.

[mawa]

Ok from the mechanical standpoint. But after calibrating the needle height I would prefer the think in "distance from the table".