empty cells

[jouke hijlkema <hylkema free fr>]

Hello all,

I'm VERY new to spread sheets and I have the following problem. I have 
data collected over a year in irregular intervals. So I have one column 
with all the days of a year and several columns with sparse data. Now I 
want to make an XY plot using splines to interpolate. This works well if 
I  select non empty cells by hand. But not if I simply select the first 
and another column. Is there a way to do this automatically ?

Jouke