"interval hour to minute" or "interval day to minute"

Hi

I discovered the 'fields' option of 'interval', but i can't figure out
from the docs how it is supposed to work. Are "hour to minute" and "day
to minute" really the same thing? And if not, in what circumstances are
they treated differently?

psql (8.4.7)
Type "help" for help.

postgres=> select '3 years 2 months - 1 day + 10 hours 5
minutes'::interval day to minute;
interval
----------------------------------
3 years 2 mons -1 days +10:05:00
(1 row)

postgres=> select '3 years 2 months - 1 day + 10 hours 5
minutes'::interval hour to minute;
interval
----------------------------------
3 years 2 mons -1 days +10:05:00
(1 row)

Warm regards
Jack Douglas