App to scale dimensions from blueprint

[Pipefitter]

I am needing an app to open pdf blueprints and have the ability to scale different dimensions. Some drawings you just can't find a dimension on and with the old school paper prints you could just pull out your tape and see how far it is. With the ipad I'm not sure how to do this. I'm sure the scale would be off since the size is different, especially with the zoom.

Thanks for any help

 

[twerppoet]

I took a look around the App Store, and this was the only thing that looked promising, but it's much more than a measurement tool, and seems to require an account:

https://itunes.apple.com/us/app/plangrid-construction-plans/id498795789?mt=8


This looked pretty good at first. It's main fault seems to be the inability to handle large PDF's. Unfortunately blueprints are often quite large.
https://itunes.apple.com/us/app/auto-measures/id494847577?mt=8