+const TimeDelta zero(0);
+const TimeDelta usec(1);
+const TimeDelta msec(1000);
+const TimeDelta sec(1000000);
+const TimeDelta min(60*1000000);
+const TimeDelta hour(3600*1000000LL);
+const TimeDelta day(86400*1000000LL);
+const TimeDelta week(7*86400*1000000LL);
+