Generation Tools’ I-Beam level gives you a long level in a short package. It incorporates three sliding rails which allow it to expand to about 2.5x its length. They claim it can be used in framing and leveling forms, and because of its construction, it even works around warped studs.
They fabricate the level from 6061 aluminum, anodize it, and then add stainless steel hardware and precision milled bubble vials. Positive lock brakes keep the level set to the length you choose.
Generation Tools manufactures three different sizes of the I-Beam levels. The first can extend from 4′ 3″ to 10′ 8″, the second from 5′ 3″ to 13′ 10″, and the third from 6′ 4″ to 17′ 4″. Pricing for the levels starts around $140.