Problem:

Calculating the number of hours that constitute each month (serial number) listed in column A.
One hour should be subtructed to April due to the shift to daylight saving time.
Similarly, one hour should be added from October\'s total due to the shift back to standard time.

Solution:

Use the DAY, EOMONTH, and DATE functions as shown in the following formula:
=DAY(EOMONTH(DATE(2005,A2,1),0))*24-(A2=4)+(A2=10)