[argyllcms] I don't understand the -u option

I produced a profile which is approximately what I would like.

I used the options

 dispcal -v -yl -qh -t6000 -b125 -g2.2 -p .7,.5,.6 -o TargetX

But it came out with a gamma of 2.8.   I would like one closer to 2.2.

So I tried

dispcal -v -yl -qh -t6000 -b125 -g2.2 -p .7,.5,.6 -u TargetX -o TargetY

TargetX.cal was updated, but nothing else changed as best I can tell.

I clearly don't understand how to use the -u option.  Can someone help me?


One other question.
I am using an Eye One Pro.  Each time I use it, I am asked to calibrate it, 
which I do using the appropriate holder.  If I make repeated attempts,
one after the other, is it okay to skip the calibration step?

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