  This paper gives a novel formula (Copenhagen Limit) to calculate/estimate the
dynamic state error of a system without a feedforward signal. Copenhagen Limit
is in the form of a limit and finds the dynamic error in an analytical
solution. It can be used to design the controller in a tracking control
problem. A numerical example is displayed to illustrate the accuracy of the
Copenhagen Limit. Besides, the controller of a UAV (quadrotor) is designed
using the Copenhagen Limit in a trajectory-tracking problem. The result of it
is also demonstrated and analyzed.
