question about surface plot

[chaofang yue]

Dear group:
   I am a new user of ImageJ. I am analyzing an image using "surface plot".
I have a couple of questions about the surface plot. First, what is the unit
for z axis?  When I make a plot, I see "pixels" for x and y axises, but not
for z. Second, is there a way I can change/assign the range (minimal,
maximal) of z axis?

Thanks a lot! chaofang