Spirit level

Manfrotto has has 3 devices that serve me well as 'levelers'.

There is a replaceable tripod column with a built in level adjust.

Next, there is a 'partial' ballhead leveler that mounts between the tripod and your ballhead.

Lastly, a rock solid dual plate with 3 screws that permits very accurate leveling. It mounts directly on the tripod and your ballhead mounts on top.

My tripod uses the replaced tripod column as it results in the least weight increase and functions quite well. Before it became available I used the dual plate leveler only because I did not notice the partial head unit in the catalogue.

An excellent test for a leveler is to mount your normal ballhead on it, level the ballhead and pan the ballhead 360° and observe for any motion in the 'bubble' in the ballhead. There should be little or none.

The tripod column was <$100 and the other 2 was ~$50, all inexpensive.

good luck irv weiner