Scaling and Hairlines

Hello,

I'm a technician who's recently moved to my employers technical publications dept. I'm trying to create a document, but having a little trouble with Designers behaviour. I'm copying vector objects from a PDF into designer, then scaling them up by 260%. We're required to have all line weights set to hairline, which I've done. The problem is that when I scale the objects up, the lines no longer appear as hairlines, even though the property manager bar shows 'hairline'.

It doesn't matter if I set the line weight before or after scaling, I get the same results.

From what I've been told, a hairline should not appear to grow in width as you zoom in.

Thanks in advance!