Brooke, Correct, with a Cs standard you can expect that there will be no long-term drift in frequency. However if you look at the short-term you will often see trends that look like drift. In your S/N 1227 plot both red and blue show trends on the order of 3 to 4 days. You are wise not to call this frequency drift.
But from my perspective, the 3 weeks of data that is both red (Loran-C) and blue (GPS) are nice lines with no parabolic component. It's not fair to "fit" a 2nd degree polynomial to 3 weeks of Cs data that has more than 50 ns of noise. For those 3 weeks, the slope of a *line* through the blue points is about -4e-13 and the slope of the red line about +4e-13. I think you have a minor sign error. One counter is measuring Cs to GPS and the other Loran to Cs, instead of Cs to Loran, or something like that. With the sign error corrected you'll also note both lines are parallel. And that both blue and red show a common bump around DOY 108. That suggests it was your Cs going off a bit for 2 or 3 days, not something unique to GPS or to Loran-C. There are other visible common-mode excursions from a linear trend as well. I can't explain the parabolic trend in blue prior to DOY 102. But it looks to me like as soon as you started Loran-C logging you've got clean, linear data from both GPS and Loran-C. Do you have data for dates beyond DOY 120 to verify this hunch? /tvb _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts