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The metric ruler is readable but that imperial side is difficult to make any sense .i am happy to work in imperial inches or metric or mixture of both.I have spent the last 50years in industry working in both. John
John.......that is a "special" ruler made like that for "metricists" to use in pictures to reinforce their disdain for the Imperial System.
Please excuse my ignorance, but is this an engine that would of been used in real life for something or is it just a really big model? Also, any guesses how old these castings might be?
Something does not look right on your drawing, the standards stick out beyond the cylinder but are overhanging the inside of the standard, photos suggest it should be one or the other.