The clock accuracy of the D-5 is +/- 3ppm, when the unit is new. The G-03x is 0.1ppm and that means that it is 30 times more accurate. I decided to get the G-0Rb (rubidium) which is accurate to 0.05 ppb which is about 2000 times more accurate than the G-03x and, if my math is correct, 60,000 times more accurate than the clock in the D-5. I will post after the clock is broken in. The reviews I have read make me comfortable with my decision.