What's the meaning of timestamp in Xcode?

I always found time stamp after running objective-c program in Xcode, but it has six number after the seconds , what’s the meaning of it?

Example

2017-04-22 19:52:13.728042 intresting name[1150:198449] Hello, World!
Program ended with exit code: 0

what’s the meaning of 728042?

2017-04-22 19:59:42.737502 intresting name[1166:204778] Hello, World!
Program ended with exit code: 0

what’s the meaning of 737502?

Probably, microseconds.