[GBrutus]

I agree with the first part of your statement, but factory blueprints are 100% accurate!!! You might not want to take into account side views where eletrical or hydraulical plants are shown, but a dimensional drawing from the factory drawing table is accurate to the millimetre (yes, even in the '30s)!!!

You're right, I was writing gibberish there. I've seen a few instances where these side views have been mistaken as being a true dimensional drawing and this is what I was getting at.