probability for the particle to be observed within these widths of wave packet is unity, and it follows a classical motion before the next measurement.

The product of uncertainties of the momentum $\Delta {\vec p}$ and position $\Delta {\vec x}$ may be much larger than that of the minimum wave packet, $$\begin{aligned}
|\Delta {\vec x}|| \Delta {\vec p}| \gg {\hbar \over 2},\end{aligned}$$ so nonminimum wave packets $\left(\text{Eq}.~(\ref{non-minumum-wave packet})\right)$ are suitable for these states.

By successive measurements, a particle’s trajectory that follows classical motion is observed [@Schiff2]. This happens because the wave packet has a finite spatial size, and the probability for this particle to be observed in the inside of this region is unity. Actually, as discussed in a previous paper,[@Ishikawa-Shimomura] the wave packet spreads with time. The spreading velocity depends on the mass and energy. For the particle trajectory to be observed, a next successive reaction with an apparatus should occur before the wave becomes large. Unless an observation is made, the wave spreads ultimately and a straight trajectory is not tested.

Because light microscopic particles spread fast, they become momentum eigenstates easily. Hence, translational invariance is preserved for these particles. On the other hand, for macroscopic objects or 