Siemens sinumerik 840D sl Operating Manual page 57

Turning
Operating Manual, 07/2010, 6FC5398-8P40-0BA0
The selected axis is marked with an "x" meaning "safely referenced"
in the "Acknowledgement" column.
By pressing the <SELECT> key again, you deactivate the
acknowledgement again.
Setting up the machine
2.2 Approaching a reference point
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