Hello:

A low cost option I use is from Home Depot. They sell flat magnetic sheets for people to place over register vents in rooms they do not want to heat or cool. I got 3 sheets for $8. this made a big difference in balance, plus they are easy to slide based on the EP weight.

Also, I took a Sharpy and wrote out the magnifications based on EP on the sheet to save me from doing the math in my head.

Scott