Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct comparisons of European primary and secondary frequency standards
  via satellite techniques   We carried out a 26-day comparison of five simultaneously operated optical
clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB
by using two satellite-based frequency comparison techniques: broadband Two-Way
Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System
Precise Point Positioning (GPS PPP). With an enhanced statistical analysis
procedure taking into account correlations and gaps in the measurement data,
combined overall uncertainties in the range of $1.8 \times 10^{-16}$ to $3.5
\times 10^{-16}$ for the optical clock comparisons were found. The comparison
of the fountain clocks yields results with a maximum relative frequency
difference of $6.9 \times 10^{-16}$, and combined overall uncertainties in the
range of $4.8 \times 10^{-16}$ to $7.7 \times 10^{-16}$.

26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
31
The categories of this paper are: ao-sci
28
The categories of this paper are: alg-geom
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
13
The categories of this paper are: quant-ph
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys