For a simple electromagnetic model of a clock introduced by Jefimenko (clock # 1 in 1996 Am. J.
Phys. 64 812), a change of the rate of the clock when it is set in uniform motion is calculated
exactly, employing the correct equation of motion of a charged particle in the electromagnetic field
and the universal boostability assumption. Thus, for the clock under consideration, dynamical
contents of the clock retardation are demonstrated. Somewhat surprisingly, the analysis presented
discloses that some familiar relativistic generalizations concerning the retardation of clocks have
to be amended.