Tom, I had made exactly that assumption with my level, which looked similar to the one Mark used. When my father-in-law saw me using the level on its side like that, he cautioned me about the potential problem. Sure enough, it was different. My other torpedo level was fine. Both were fairly new (10 years at the oldest), so I don't know if it was an "old vs. new" issue, or a "cheap vs. expensive" issue. A quick check before you leave the store will put all doubt to rest.