Subroutines with data arrays transferred to or obtained from GreG have a Real*4 and a Real*8 version. The simple precision has a name beginning by GR4_, the double precision a name beginning by GR8_. In the argument list description, REAL will mean Real*4 for the GR4_ version, Real*8 for the GR8_. These routine work by copying the data. For really big arrays, it is more efficient to transfer the information by reference, though SIC variables (see the SIC manual).