Try this; The Common Cents System
After you browse the site and understand the instructions here is some material Copied from another source...........
1. Trap your rod by the handle parallel to the floor with the tip of the rod more than 1/3 the rod's length, higher than the floor. For example, you need to have the rod parallel to the floor and more than 3' off the floor for a 9' rod. I'd give it a foot to spare.
2. Take a small paper clip and unbend one end so it makes an 'S' shape. Find a small plastic bag.
3. Hang the plastic bag from the rod tip using the 'S' shaped clip, and then measure the distance from the tip to the floor and be precise.
4. Put pennies that are shiney and newer than 1996 into the bag till you have bent the rod tip to 1/3 the length of the rod from the measurement you got in step 3.
5. So for an easy example, lets say in step 3 you had a 9' rod and got a measurement of exactly 4.0 feet from the tip of the rod to the floor. Then in step 4 you got enough pennies in the bag to get a measurement of precisely 1.0 feet from the rod tip to the floor. Take the pennies and count them. For this example lets say you are testing an Orvis 'Zero Gravity Midflex' 5 wt., 9' rod. The number of pennies you count will be 53. This gives you an ERN, or actual rod weight of 6.5.
I would avoid the new nonstandard pennies, as I am not sure they are using the same slug to stamp them as the old style pennies. If they do any penny newer than 1996 is good as long as it is still shiney. This works because there is a known weight for these pennies.