Ignore Future Data In A Chart

[CROY1985]

Hi All

I am setting up a sheet which will help each our companys centres monitor electricity usage. I have a table set up as below:

Column A
Week Ending
01/04/11
08/04/11
...
23/03/12

Column B
Meter Reading

Column C
Usage
=IF(B3=0,"",B3-B2)

I have set up a line graph, linked to columns A and C of the table, but it is plotting the line at zero right through to the end of the chart. I want it to only plot the line for the weeks in which we have usage figures - is this possible?

Thank You

 

[CROY1985]

Update, i have also added formula to column a to keep cells blank unless there is a meter read for the week. this is what ive used.

=IF(B2>0,A1+7,"")