I found my answer at a previous post:
jc113883 Posted: Monday, December 20, 2010 7:45:54 PM
I had to see it with new eyes this morning.
I only had to tweak the following line,
MyDataset.Expression = "'tagname'*2"
If anyone does get to read this, if I want my expression to be MyDataset.Expression = 2*2
then it does not recognize the column Value somehow.
I must go in the trend via gui (manually) and click the Expression, then click the box for Column, and then I'm ok to move on.
This just seemed strange.
Anyhow, overwriting the Values works, and I am happy!