Is number after DateTime2 is for nanosecond purpose?

I have read the 开发者_开发技巧document already but i do not fully understand The default precision is datetime2(7) is 7 represent the precision of nanosecond?

No, the number represents the number of digits preserved after the decimal point for the seconds. 3 would be millisecond, 6 microsecond and 7 equivalent to a precision of 100 nanoseconds.

The resolution of the default precision (7) datetime2 type is 100 nanoseconds.

An excellent reference for things date/time is : The ultimate guide to the datetime datatypes