Ok, sorry. Forget about the point 2. I just found out how to use parameters. Still need help to get a smooth line though!
I'll answer the easier one first,
2) Use a parameter.
1) Smoothing is definitely a possibility in Tableau. However, calculating once every certain number of places causes some issues. Refer to Sheet 1 attached.
A better bet is to use a rolling average in order to smooth your graph. Refer to Sheet 2 attached.
Hope this helps,
Book2.twbx.zip 401.0 KB