math - Why should I use t1 - t0 < 0, not t1 < t0, when using System.nanoTime() in JAVA -

when reading system.nanotime() api in java. found line:

one should use t1 - t0 < 0, not t1 < t0, because of possibility of numerical overflow.

http://docs.oracle.com/javase/7/docs/api/java/lang/system.html#nanotime()

to compare 2 nanotime values

long t0 = system.nanotime(); ... long t1 = system.nanotime(); 

one should use t1 - t0 < 0, not t1 < t0, because of possibility of numerical overflow.

i want know why t1 - t0 < 0 preferable way prevent overflow.

because read other thread a < b more preferable a - b < 0.

java integer compareto() - why use comparison vs. subtraction?

these 2 things make contradiction.

the nano time not 'real' time, counter increments starting unspecified number when unspecified event occurs (maybe computer booted up).

it overflow, , become negative @ point. if t0 before overflows (i.e. large positive), , t1 after (very large negative number), t1 < t0 (i.e. conditions wrong because t1 happened after t0).....

but, if t1 - t0 < 0, well, magic same overflow (undeflow) reasons (very large negative subtract large positive underflow), result number of nanoseconds t1 after t0..... , right.

in case, 2 wrongs make right!