How to subtract tag from tag and store as historian variable

Maker
1

Hi there,

I'm reading 2 tags, which I want to subtract val_A from val_B, and store the result as historian so that I make a graph from the last hour. How can I achieve this?

2

Expression tag with historian enabled.

3

Create an expression tag and set the expression to something like,
{[~]Val_B} - {[~]Val_A}