Problem with the Pre-projected data

[Hui Du]

Hi everyone,
I have some pre-projected data(netcdf format) from mm5. For correctly
displaying them,
I used the following grads script:

DSET ../cal.controlb.1dom.nc
DTYPE netcdf
TITLE controlb
UNDEF 99999.0
PDEF 88 68 lcc 37.25 -121.75 44 32 34 69 -121.5 30000 30000
XDEF 88 LINEAR 223.6738 0.3447
YDEF 68 LINEAR 28.4976 0.2758
ZDEF 1 LEVELS 1
*TDEF 1 LINEAR 12Z1jan1959 1dy
TDEF 1697 LINEAR 00Z1aug1995 6hr

When I open this 'ctl' file in grads and 'q dim', I got the following

Default file number is: 1
X is varying Lon = 223.674 to 253.663 X = 0.99996 to 88
Y is varying Lat = 28.4976 to 46.9762 Y = 0.999995 to 68
Z is fixed Lev = 1 Z = 1
T is fixed Time = 00Z01AUG1995 T = 1

I think X and Y should be always integer. why are X and Y numbers with
point?

Also I got some points's values missing for the new grid(the second
grid) when I plotted
Can anyone give me some hints for this problem?
After looking up the documentation, I am still confused.
Thanks a lot

Hui