An awkward code question.

Code:
int64_t CVideoReferenceClock::GetTime(bool interpolated /* = true*/)
    ...
    return CurrentHostCounter() + m_ClockOffset;

I add log find that m_ClockOffset is always changing, and can not find where the m_ClockOffset is changed.
There are only two places can change the m_ClockOffset in the source code.
1.void CVideoReferenceClock::Start()
But can only be run once.
2.void CVideoReferenceClock::Process()
But is not run.

Who can tell me where the m_ClockOffset is changed?
Thanks!