Added by zhenyu han almost 8 years ago
in the old version(v1.6.5 used), the time unit is "hours since 1949-12-01 00:00:00" .
but in the v1.7.0 the unit is changed to "hours since 1949-12-1 00:00:00". so the length of string is not fixed, when date change from 1 to 30.
this cause some trouble, because in all my Fortran code, the length of units string are all fixed.
hope the time unit could still use the old format in v1.6.5