PaulS, that is the RTCM Special Commitee 104 standard for Earth Centered Earth Fixed antenna position cooordinates. I,m just trying to make the actual measurement fit into their critera.
So what your saying is there is no way to directly work with 64 bit numbers on the 8bit AVR MCU?
I was thinking of moving up to a 32bit AVR with built in FPU but I didn't want to spend on having custom circuit boards made untill I had figured out how to make it work on something I was somewhat familiar with.