### SLA_DTT

TT minus UTC

ACTION:
Compute $\Delta$TT, the increment to be applied to Coordinated Universal Time UTC to give Terrestrial Time TT.
CALL:
D = sla_DTT (DJU)
##### GIVEN:
 DJU D UTC date as a modified JD (JD$-$2400000.5)

##### RETURNED:
 sla_DTT D TT$-$UTC in seconds

NOTES:
(1)
The UTC is specified to be a date rather than a time to indicate that care needs to be taken not to specify an instant which lies within a leap second. Though in most cases UTC can include the fractional part, correct behaviour on the day of a leap second can be guaranteed only up to the end of the second $2{3}^{h}\phantom{\rule{0.3em}{0ex}}5{9}^{m}\phantom{\rule{0.3em}{0ex}}5{9}^{s}$.
(2)
Pre 1972 January 1 a fixed value of 10 + ET$-$TAI is returned.
(3)
TT is one interpretation of the defunct time scale Ephemeris Time, ET.
(4)
See also the routine sla_DT, which roughly estimates ET$-$UT for historical epochs.