Problem with redefining the axis

["Min, Dughong" <min@xxxxxxxxxxxxxx>]

Hello, Ferret Users;

Sorry to bother you with an easy question. (^_^)

What i want to do is to replace temperature values
in original Z axis of the netcdf data file with those on 
new depth axis. 

That is, an original data file has
depth   temp
   20       25
   40       24
   60       23
   80       22
  100       21

I expect to replace the above into
  depth   temp
   10         25
   30         24
   50         23
   70         22
   90         21

Therefore, I have done follwing 
yes? let lev={10.00,30.00,50.00,70.00,90.0]
yes? define axis/from_data/depth/Z/name=nlev/units=meters lev
yes? plot temp[gz=nlev]

Unfornately,
my problem is that new defined "temp[gz=nlev]" displays  
the interpolated values of the original data on new z axis 
which may be related to dynamic axis.  
yes? list temp[gz=nlev]
   depth    temp
     10         ....
     30        24.5
     50        23.5
     70        22.5
     90        21.5

I want to change only z depth axis to new axis with 
data keeping.
I am really appreciated of any comments on how to solve my problem....

Thank for  your help in advance.
Duke Min