Hi all... I tried to calculate vertical temperature gradient of upper ocean. I want to know whether ferret recognizes the depth axis as that of postive value 0, 50m, 100m or negative values 0 -50 -100.....when ferret calculates vertical gradient. So if ferret recognizes like the former, when I calculate the gradient, it should be dtdz = -1.0*temp[z=@ddc] -Seon-