The drive current refers to the current which flows through the quartz crystal unit. If an excessive drive current is applied to the quartz crystal unit, it involves the risk of giving rise to such non-conforming phenomena as those described below:
i.	Increase in electromagnetic wave noise.
ii.	In the case of "TUNING FORK", branch breaking occurs.
iii.	Variations occur in the characteristics of the quartz crystal unit. (Frequency variations, equivalent series resistance variations, etc.)
iv.	In extreme cases, it may even lead to breaking the quartz crystal unit.