The seven current, proposed and/or soon to be implemented measures of physics are:
Originally the second was 1/(24 * 60 * 60) of the day ; a problem was the Earth's rate of rotation was found to be slowing down. There were others so now:
"The second, s, is the unit of time; its magnitude is set by fixing the numerical value of the ground state hyperfine splitting frequency of the caesium 133 atom, at rest and at a temperature of 0 K, to be equal to exactly 9 192 631 770 when it is expressed in the unit s^-1, which is equal to Hz."