Oracle-numtodsinterval&numtoyminterval

select sysdate now,
sysdate+numtodsinterval(1,'second') add1second,
sysdate+numtodsinterval(1,'minute') add1minute,
sysdate+numtodsinterval(1,'hour') add1hour,
sysdate+numtodsinterval(1,'day') add1day,
sysdate+numtoyminterval(1,'month') add1month,
sysdate+numtoyminterval(1,'year') add1year,
sysdate+numtodsinterval(-1,'second') subtract1second,
sysdate+numtodsinterval(-1,'minute') subtract1minute,
sysdate+numtodsinterval(-1,'hour') subtract1hour,
sysdate+numtodsinterval(-1,'day') subtract1day,
sysdate+numtoyminterval(-1,'month') subtract1month,
sysdate+numtoyminterval(-1,'year') subtract1year
from 
dual