New tag with Python script?

Hello Forum,
is it possible to create a tag which will run a python script and calculate differences from other tags?
what kind of display do i have to use? (label , numeric label etc) in order to see the data from the script.
do i have to create the tag on the ignition designer or on the gateway?

many thanks!

Tags live on the Gateway but are typically created using designer.

If you’re looking for a tag that calculates the difference between two other tags it will be much simpler to use an expression tag. The below link has a description and video to explain it.

You can then use this tag with a numeric display to visualize it for an operator, or just see the value in the Tag Browser if that’s all you need to do.

Thank you Bryan

i created the expression tag as value source expression and data type float but in the expression can i write python?
when i write anything as a script inside i see a red X which indicates a bad tag.

Expression language differs from Jython.

The expression language addressed by @BryanB and @JordanCClark is great for simple calculations but if your calculation is more complex, you will want want a tag event script.
You can write a python script that will execute whenever the value of one the tags of interest changes.
Write the result of the calculation into a third tag that is displayed to the user.

Take a look at Inductive University Tag Event Scripts: