I'd like to format for number for time to figure out total time of particular task like stop watch in second.

example; A1,B1 and C1 all formatted to hh:mm:ss
Enter start time in A1 then enter finish time in B1
C1 is formula =B1-A1

Result is all column show only hour and minutes, second is always 00. Like,,

12:20:00 12:23:00 00:03:00

How to set second section to be shown?? like ,

12:20:25 12:23:48 00:03:23