Specific meanings of jstat parameters : YGCT FGCT GCT

I need to use jstat to measure some GC parameters of a program. Jstat provides set of parameters ( S0C S1C S0U S1U EC EU OC OU MC MU CCSC CCSU YGC YGCT FGC FGCT GCT) From those I am bit confused with the descriptions for YGCT, FGCT and GCT.

(YGCT Young generation garbage collection time.
FGCT Full garbage collection time.
GCT Total garbage collection time.)

I have 2 questions.

1) What does these three parameters (YGCT, FGCT and GCT) actually measure? A small comparison would be very helpful

2) I how can I know the unit of time that they are mentioning? (milliseconds/ seconds/.... )

I referred many documentations including

Interpreting jstat results
http://www.cubrid.org/blog/dev-platform/how-to-monitor-java-garbage-collection/
http://docs.oracle.com/javase/6/docs/technotes/tools/share/jstat.html#output_options
But these does not answer my real question.
Could anyone how has experienced with jstat help me with this?

Thank you.

• YGCT - Seconds spent in young generation collections since the JVM started
• FGCT - Seconds spent doing full garbage collections since the JVM started
• GCT - the sum of the above two values

This knowledge comes from experience and testing - I have not found a good reference defining the time unit and exact meaning.