What tool is normally used to check the alignment on the horizontal seams of the shell plates?

• A. A laser level
• B. A spirit level
• C. A plumb bob
• D. A 2-foot level

Answer: (D)

To check how shell plate seams sit, you need a tool that shows whether the surface is truly horizontal across the seam. A level that spans the seam gives a direct, easy-to-read indication of any rise or dip from side to side. The two-foot level is a common choice because its length is long enough to cover typical seam gaps but still easy to maneuver on the curved shell, providing a clear bubble reading that tells you if the seam is level. A plumb bob measures verticality, not horizontal alignment, so it doesn’t help with checking horizontal seam alignment. A laser level could be used, but in many workshop and field setups the straightforward bubble reading of a two-foot level is faster and more reliable for this specific task. A general spirit level works in the same way, but the two-foot level is the standard tool for spanning the seam and reading the bubble accurately across the line.