Displaying YTD totals as you populate monthly information

[Guest]

I have a worksheet with a "YTD" use table which is fed from information on a
secondary monthly meter reading table. The YTD subtracts the current month's
reading from the prior month's reading.

The problem is once I enter the actual use for one month, say Dec. then Jan
YTD shows that meter reading since there is no data for Jan in the use table
yet. My YTD formula (in essence) says subtract Jan reading from Dec reading
to get an amt used. Is there any way to keep the YTD from displaying the one
month's reading until both month's have been entered to get the actual use?

 

[Fred Smith]

Use the If function to check for data in the cell first, as in:

=if(b1="","",b1-a1)