I want to make normalize my time evolution compared to time at start.

From the following the dataset:
Date val
D1 v1
D2 v2
D3 v3
D4 v4

should produce
Date val
0 v1
D2-D1 v2
D3-D1 v3
D4-D1 v3

If I do the normal difference operation I get --. I suppose the format are wrong.
I use Origin 5.0, and the dd-mm-yy hh:mm:ss format.

Thanks

Thanks a lot it works very well.-)
The solution was so easy.

Thanks again