現今使用網路時間通訊協定(Network Time Protocol) 的校時軟體均有兩種校正時間的方式。當時間誤差大時會直接校正時間，也就是將客戶端系統時間直接調整為伺服器的時間，針對此狀況過去的研究已提出利用熵的時脈偏移測量方法來進行正確測量；而當時間誤差較小則校時軟體調整客戶端的時脈或分段調整時間來逐步達到正確的時間，這種校時模式耗時較長，而且會導致錯誤的時脈偏移測
量值。由於現今硬體製造技術進步且大多數連網設備每24 小時即進行同步，因此大部分的情況下時間誤差均為後者的情形，因此本研究針對這種情況下的時脈偏移量測提出方法。
本研究比較最常見的校時軟體ntp 與chrony，針對校時所需時間去做考量，測試了在相同時間差下，所需要的校正時間。另一方面，我們也觀察到chrony 伺服器搭配適當參數的情況下，時間偏移量的分佈圖會呈現階梯狀分布，也因此可以利用分段式演算法DROML(Dynamic Region of Offset Majority Locating) 測量時脈偏移。
本研究貢獻在於透過研究校時軟體chrony，發展出不論校時前時間誤差為何，
均可以在校時過程中測量時脈偏移的方法。相較於未校時的時脈偏移值，校時過
程中的測量誤差均不高於3ppm。

The synchronization software over NTP (Network Time Protocol) supports two approaches of time synchronization. When the time difference between client and tim server is larger than some threshold, the system time of client will be directly set to the time of server site; Otherwise, the time synchronization software slightly altered the time or clock ticking rate to eliminate the amount of offset gradually. Entropy-based approaches are able to provide precise measurement for the former cases, but the measured clock skews in the later cases was never correct, and unfortunately most time synchronization belongs to the later cases. Therefore, this work aims at solving this issue.
We studied the most common two time synchronization software ntp and chrony,
including their patterns in later cases and the amount of time required upon the same amount of time difference. We observed that the scatter diagram of time offset during time chronization process become a series of cascade when chrony is used with appropriate parameters. The kind of pattern can be correctly solved by algorithm supporting multisegment measurement like DROML (Dynamic Region of Offset Majority Locating).
The contribution of this work is to develop an approach based on chrony such that the clock skew is still measurable during time chronization process. Comparing to the normal condition, the observed errors of the proposed approach are bound to 3 ppm.

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