I want to note a day change

[Fred1]

I have a spreadsheet to log battery life between charges. I want to note a day change and subtract 8 hrs. (sleep time) if the day has changed. Currently I am using IF(DAY(B2)-DAY(A2)>0,-8). This works fine except for the first day of the month. See below

Day1	          Day2	            Diff	        Diff	    If
date time	    date time	        DAY(B2)-DAY(A2)	DAYS(B3,A3)	IF(DAY(B2)-DAY(A2)>0,-8)
29/09/13 18:20	30/09/13 08:20	    1	            0.5833333333	-8.00    Correct
30/09/13 18:20	01/09/13 08:20	   -29.00	       -29.4166666667	0.00     Wrong

Any Ideas?

[JohnSUN]

May be =INT(B2)-INT(A2)?
But please keep in mind that the function IF() without the third parameter (ELSE) can lead to incorrect results.