Consider an inexpensive laser level mounted on a level tripod. My kids got me one as a gift eight years ago and now everything in the house is level, including bike seats (actually I've got the nose of the Sella Italia SLK's up 2 degrees and the rest are level).
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831