Table 7. Mean fractional deviation of the TAI scale interval from that of TT The fractional deviation d of the scale interval of TAI from that of TT (in practice the SI second on the geoid), and its relative uncertainty, are computed by the BIPM for all the intervals of computation of TAI, according to the method described in ‘Azoubib J., Granveaud M., Guinot B., Metrologia 1977, 13, pp. 87-93’, using all available measurements from the most accurate primary frequency standards (PFS) IT-CSF1, IT-CSF2, NICT-CSF1, NIM5, NIST-F1, NIST-F2, NMIJ-F1, NPL-CSF2, NPLI-CSF1, PTB-CS1, PTB-CS2, PTB-CSF1, PTB-CSF2, SU-CSFO2, SYRTE-FO1, SYRTE-FO2, SYRTE-FOM and secondary frequency standard (SFS) SYRTE-FORb consistently corrected for the black-body radiation shift. In this computation, the uncertainty of the link to TAI has been computed using the standard uncertainty of [UTC-UTC(k)], following the recommendation of the CCTF working group on PFS. The model for the instability of EAL has been expressed as the quadratic sum of three components: a white frequency noise 1.7 × 10**-15 / sqrt(t) in 2013 and 2014 and 1.4 × 10**-15 / sqrt(t) in 2015, a flicker frequency noise 0.35 × 10**-15 in 2013 and 2014 and 0.3 × 10**-15 in 2015 and a random walk frequency noise 0.4 × 10**-16 x sqrt(t) in 2013 and 0.2 × 10**-16 x sqrt(t) in 2014 and in 2015, with t in days. The relation between EAL and TAI is given in Table 5. Month Interval d/10-15 uncertainty/10-15 Jan. 2013 56289-56319 -0.09 0.20 Feb. 2013 56319-56349 +0.11 0.22 Mar. 2013 56349-56379 +0.57 0.22 Apr. 2013 56379-56409 -0.16 0.21 May 2013 56409-56439 -0.27 0.19 Jun. 2013 56439-56469 +0.05 0.24 Jul. 2013 56469-56504 -0.39 0.21 Aug. 2013 56504-56534 -0.61 0.26 Sep. 2013 56534-56564 +0.30 0.25 Oct. 2013 56564-56594 +0.29 0.21 Nov. 2013 56594-56624 +0.32 0.21 Dec. 2013 56624-56654 -0.42 0.24 Jan. 2014 56654-56684 +0.32 0.25 Feb. 2014 56684-56714 -0.27 0.20 Mar. 2014 56714-56744 -0.64 0.21 Apr. 2014 56744-56774 -0.49 0.19 May 2014 56774-56804 -0.83 0.21 Jun. 2014 56804-56834 -0.86 0.23 Jul. 2014 56834-56869 -0.29 0.22 Aug. 2014 56869-56899 +0.42 0.19 Sep. 2014 56899-56929 +0.20 0.18 Oct. 2014 56929-56959 +0.37 0.20 Nov. 2014 56959-56989 +0.64 0.26 Dec. 2014 56989-57019 +0.48 0.25 Jan. 2015 57019-57049 +0.08 0.27 Feb. 2015 57049-57079 -0.48 0.24 Mar. 2015 57079-57109 -0.18 0.23 Apr. 2015 57109-57139 -0.14 0.23 May 2015 57139-57169 +0.34 0.21 Jun. 2015 57169-57199 +0.81 0.18 Jul. 2015 57199-57234 +0.52 0.25 Aug. 2015 57234-57264 +0.31 0.26 Sep. 2015 57264-57294 +0.07 0.21 Oct. 2015 57294-57324 +0.26 0.24 Nov. 2015 57324-57354 +0.05 0.31 Dec. 2015 57354-57384 +0.01 0.37