Whats the best way to level heights on concrete fence posts

Hi all,

Loads of info about setting up string line, digging post holes, levelling both verticals, etc..But cant really find much about how to level between the tops of the posts.

Whats the easiest way that people have used? Assuming ground is reasonably level, digging down 2ft, there will still be some variation between the levels of the post heights.

Do people just estimate and go with this slight variation? Or is there a more accurate way to do this?

Long timber across the tops with a level on top for the first two posts and then string line across the top to the last post and work to that?

Any tips appreciated.

Thanks.

 

Using a water theodolite works well enough.

Instruction here http://www.instructables.com/id/-WATER-TUBE-LEVEL-from-scraps-/

The article suggests an inner tube from a bicyle wheel. Instead using a hose pipe allows for very long distances between posts. Ensure there is no air trapped in the hose pipe.