"Adjustment" > Z-offset

During a print, I have a button that says “Adjust”. The first option after that is pressed is “Z-offset”.

I know what it does or at least the intent - it compensates for the difference between the exact height of the nozzle and the height as reported by my BL touch. It looks (roughly) like this;

<=Z- [-0.70] +Z=>

What I’m struggling with is the exact mode of operation as follows;

If the Z value shown in the middle is negative, does that mean the nozzle is higher than the BL touch or lower?

I know clicking “<=Z-” will reduce the [-0.70] to [-0.71] - so yeah, it’s decreasing the Z value - but is that moving the print head closer to or further away from the bed?

So confused!

If it works like my Enders it will be moving the nozzle down towards the bed.

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That would be logical; Z- meaning negative travel on the Z axis, which is oriented Zmax at “Top” and Zmin at “Bottom”.

I think it also matches my recent experience of having to change Z-offset due to a strip-down, clean and re-tighten. My printer originally had a Z-offset value in the box of -1.48. I did the maintenance and noticed the BLTouch seemed to be sitting “too low” (closer to the bed, further from the nozzle), meaning the BLTouch was detecting the bed “too soon” and leaving the nozzle flying.

It had been a while since I had used the printer so at this point I had a bit of a memory lapse of how to adjust the z-offset. Instead I added two washers to my BLTouch mount (I don’t have a clever adjustable mount, just screws, washers and an apparently endless amount of “fiddling about”) moving it further from the bed, but closer to the nozzle.

So close that the nozzle touched the bed.

I then remembered the z-offset feature is only accessible during actual live printing (why, firmware gods, why?) and that is how the Z-offset came to be -0.70.

I MUST have pressed “Z+” to change this value, as pressing it now moves the Z-offset from -0.70 to -0.69, so…yeah, that’s the answer - “Z+” moves the nozzle further from the bed and “Z-”, closer.

Thanks Bonfireman for helping me get that straight in my head!