Dear ferret users, I copied the mixid layer depth script from mail archives. I tried to calculate the mixed layer depth. But it writes all values as undefined. the script is as follows: USE ptemp5801.nc show data currently SET data sets: 1> ./ptemp5801.nc (default) name title I J K L PTEMP Potential Temperature 1:192 1:128 1:32 1:528 let diff = ptemp - ptemp[k=1] + 0.5 let mld = diff[z=@loc:0] set r/i=1:192/j=1:128/k=1/l=1:528 save/file=mixlay5801.nc mld please help me in finding the mixed layer depth. Ramesh