time coordinates on the tcg scale are conventionally specified using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the earth. specifically, both julian dates and the gregorian calendar are used. for continuity with its predecessor ephemeris time, tcg was set to match et at around julian date 2443144.5 (1977-01-01t00z). more precisely, it was defined that tcg instant 1977-01-01t00:00:32.184 exactly corresponds to tai instant 1977-01-01t00:00:00.000 exactly. this is also the instant at which tai introduced corrections for gravitational time dilation.