So letís say you need to measure the thickness of something where you have access to both sides, but theyíre physically separated by partitions and other obstructions.
In my case, I want to measure the thickness of the fiberglass in a boat hull down by the keel. I can access both sides, but there are many obstructions that would prevent the use of any normal types of measuring tools.
One should be able measure this from each side and then compute the thickness.
(A) establish two parallel planes or lines (string lines will work or two straight boards) located above and below the area you wish to measure. Measure this distance, this will be dimension "A".
(B) cut a template which will allow you to bypass the obstructions. I've shown a simple arc but any shape will do (it can have multiple bends as long as it is a rigid template) and you can verify the distance from end to end (the contact points) of the template. This will be dimension "B".
(C) Measure the distance from the lower string line to the bottom of the hull where you wish to know the thickness. This will be dimension "C".
(D) Using your template, position the lower contact point at the desired location, swing the upper contact point back and forth as required to obtain the shortest measurement between that contact point and the upper string line. This will be dimension "D".
(E) Now you have all the information needed to compute the actual thickness.
Sounds a lot harder than it actually is. This is very similar in how a CMM (coordinate measuring machine) can reach in and around a casting or other object to get measurements. Only difference is you are substituting the template for the CMM capabilities.