24" level does it work

Easy to make and more accurate than a laser level, can even level around blind corners.

You can have the most expensive level made. But $10 off clear hose a little tap water can't be beat especially for what your doing.

It is just as accurate as you can read it. If you continue around back to the starting point I will put money on it that your marks won't line up.

As others have said - Water Level.

Harry K

For this job you definately want to use the water level that Ray points you to-

If you just had one spot where you needed to 'extend' your 2 foot level-- use the straightest board you can find-- then turn it over and see if it reads the same.

It sounds like you are going to try to level post #2 from post #1. No matter what method or tool you use don't make that [common] mistake. Pick a point and make all your measurements from that point. As long as you get the bubbles out you can use a 50' piece of tubing in that bucket & tubing level. [from the sounds you can probably do your deck with a 20' piece.]

Jim

Get you some clear plastic tubing put some water in it and you have your level that is absolutely correct (water seeks its level). Get the picture?. Besure the ends of your tube are open and the water in one end will be perfectly level with the water in the other end.

Just use a garden hose. Fix one end at the known height and put the other end a little bit higher and fill with water. Lower the unknown end until water added just crowns the top of both ends. Or get real fancy and add a foot of clear to each end.

Yea - Water levels are good for this, as others have said.

Other options

-Transit

- String level (Sag is a problem over a long distance and not a great choice)

- laser level - This is what I would use (I have one already) B&D ones are cheap and will do the trick

For what it's worth, if you do that, and then split the difference, you generally end up pretty damn close.

But a water level is still a better idea.