  Continuous clocks, i.e. the clocks that measure time in a continuous manner,
are regarded as an essential component of sensing technology. Precision and
recurrence time are two basic features of continuous clocks. In this paper, in
the framework of quantum estimation theory various models for continuous
quantum clocks are proposed, where all tools of quantum estimation theory are
employed to seek the characteristics of clocks with high precision and long
recurrence time. Then, in a resource-based approach, the performance of the
proposed models is compared. It is shown that quantum clocks based on $n$
two-qubits system not only can have better precision than quantum clocks based
on $2n$ one-qubit system but also support long recurrence time. Finally, it is
shown that while employing the number of $n$ entangled qubits improves the
precision of clocks by a factor of $1/\sqrt n $, it inevitably worsens the
recurrence time of the clock.
