Resting current postilion to ZERO

What line command do I send to make the current head position to X0 Y0 Z0? I found I link that seems to explain this, but it did not work.

Imported from wikidot

M306 X0 Y0 Z0

Thanks for the reply Craig, but when I enter in that cod I get the following error:

error: Axis X must be homed before setting Homing offset

I home all axis and then set the machine to X0 Y0 and Z0. Then type the M306 command. I have the X0 and Y0 positions marked on my bed and I use a sheet of paper to get the Z0. My X and Y positions haven’t changed in months, but the Z position does vary slightly.